"
Wait, what? But, there's no Gym Leaders. And the Captains don't give TMs nor the Kahuna."
Indeed, since Gen VII's super mechanic was the super move Z-Moves, instead of being given TMs you were rewarded Z-Crystals for completing the Trials. And, while it would be interesting to examine the progression of Z-Crystals/Moves you get (thinking about it already it's odd you get the Bug and Flying so late; maybe for another time), that doesn't the Island Challenge is completely devoid of TMs. While you're not directly given them, either in or around the Trials there are TMs which many either are the same Type as the Captain/Totem Pokemon or meant to help against them. Stretching the theme? Maybe, and if you feel that way you can just skip ahead, but I feel it's worth a peek:
Trial: Verdant Cavern
Captain / Type: Ilima / Normal
Totem: Gumshoos (Sun) / Alolan Raticate (Moon):
TM: Brick Break (found during Trial) & Thief (In Totem's Den, need Tauros Charge to get)
Whoa, Brick Break, THIS early? That's a very good and decently TM for the FIRST
Gym Trail. Obviously it's meant to help with the Totem Pokemon (though, in a way, I guess it could also represent Hala? I could see Hala using his sumo to break something if he was so inclined; could stretch it to even relating to the Ride Pokemon he gives player access to, Tauros Charge), both weak to Fighting no matter which version you got (though you could probably OHKO Alolan Raticate with a Pokemon with a strong enough Attack). Though looking at the other Fighting TMs, I'm wondering if it was picked out of no better option. Despite being made a TM last gen, Rock Smash was removed from the list and the only other damaging ones is Focus Blast (lol, no) or Low Sleep (which has an awkward distribution due to it being a kicking/leg move).
Special mention to Thief, which fits Alolan Raticate as it's both a Dark-type and a thieving Pokemon, but not sure about Gumshoos. That said, Thief is something I would expect to be given out at a first Gym. Low power but has a handy secondary effect if you know where to use it. Doesn't really help out with the next few set of bosses, though; and by the time Dark would be a useful Type I think Thief wouldn't be that high enough of Power to use anyway.
Grand Trial/Type: Hala/Fighting
TM: False Swipe (from Kukui after battle)
BTW, Hala is going to be the only Kahuna on here as the locations of the other Grand Trials don't have any TMs directly related to the Trials.
Though, I say this as if the TM you get after defeating Hala has anything to do with him. Nah, it's just False Swipe, given by Professor Kukui to help you with registering more Pokemon to Rotom Dex. However I decided to include it as I found it funny that during the Normal-type Trial you get a Fighting-type TM and after the Fighting-type Trial you get a Normal-type TM. Hey, eitherway you now have two TMs to use with your Normal- and Fighting-type Z-Moves!...
Trial: Brooklet Hill
Captain / Type: Lana / Water
Totem: Wishiwashi (School Form)(SM) / Araquanid (USUM)
TM: Scald (SM) / Charge Beam (USUM)
Scald at third trial (or second if you count the Grand Trial as their own thing)! The Totem's Level is 20, your Starter is still in the early levels of its Mid Stage! Not that the other Water TMs wouldn't also be a bit OP: Surf and Waterfall (besides they had a funny little joke with those two being TMs now); there was also Rain Dance but it and the other Weather Moves were on sale in Royal Avenue; wouldn't feel right to separate one from the group and a bit of a hassle to now found 3 other locations appropriate for the others.
Interestingly enough this was one of the TMs that was swapped around in USUM. Instead of Scald it's now Charge Beam, a handy if low powered Electric Move to help with the new Water Totem (though overall weaker in stats, Araquanid's part Bug-type meant Grass isn't going to cut it anymore, sorry Bounsweet trade). Though it's funny, Charge Beam was original on Route 5 (it was replaced by nothing though there are other TMs on Route 5), Scald was moved to Ancient Poni Path where Frost Breath was, and Frost Breath was moved to Seaward Cave for no particular reason. Maybe they realized how insane Scald this early was and decided to give a reason to explore Seaward Cave... even though in USUM you need to visit Seaward Cave for a Ultra Recon Squad encounter.
Trial: Wela Volcano Park
Captain / Type: Kiawe / Fire
Totem: Salazzle (SM) / Alolan Marowak (USUM)
TM: Rock Tomb
Hello Rock Tomb, you're coming in a bit late. I get it, at least in the original SM, Salazzle is fast so Rock Tomb is not only Super Effective but also decreases its Speed. But, now that we've gotten a Z-Crystal which has a Type advantage over a boss, if you were going to use any cheesing strategy it would be training a Water-type to nuke Salazzle with a Hydro Vortex. I suppose this could be one reason why they swapped it out for Alolan Marowak, it's more bulky so could likely survive a Hydro Vortex, of course since its slow that makes the Rock Tomb TM feel even less useful. Couldn't at least upgrade it to Rock Slide? It's part Ghost now, how about Shadow Ball/Claw or Dark Pulse? Then again, the only reasoning I'm even suggesting those is that they spoiled us early it now feels like a let down when they're giving us TMs which are actually about the level we're at.
Trial: Lush Jungle
Captain / Type: Mallow / Grass
Totem: Lurantis
TM: Grass Knot (found during Trial) & Smart Strike (from Kukui after Trial)
I know what you're thinking, "oh goodie, Grass Knot, Energy Ball eat your heart out", BUT unlike previous handouts of Grass Knot such as from Ramos of Kalos, coming up is Rock-type Kahuna Olivia and newly appointed Ground-type Kahuna Hapu; both who tend to use heavy Pokemon. Of course once you have Machamp Shove you should head back to Lush Jungle to get Energy Ball, but until then Grass Knot could suffice if you have no better option for Grass-type moves against an upcoming boss.
Speaking of Olivia, Kukui doesn't say it, but that's likely why he just randomly gives you Smart Strike (not sure why he/GF feels this is the only Kahuna we should get a helpful TM for; Could have given us Aerial Ace for Hala at least). Smart Strike is alright if you need a decent Steel-type move, and your Pokemon had a horn (it's called "Smart Horn" in Japanese, not sure why they felt they needed to change it. I would have actually dropped the "smart" part and called it something like "Target Horn" or, if they wanted the alliteration, "Honing Horn").
Trial: Hokulani Observatory (Mount Hokulani)
Captain / Type: Sophocles / Electric
Totem: Vikavolt (SM) / Togedemaru (USUM)
TM: Volt Switch (on Mount Hokulani) & Snarl (from defeating Route Leader/Z-Trainer Veteran Akira)
More than halfway through the Island Challenge now. Volt Switch nor Snarl isn't that exciting. Volt Switch could give an Electric-type on your team a get-out-of-dodge against unfavorable match-up while also doing some damage, BUT since that doesn't work on Ground-types your Electric-type likely already has a normal Electric-type move serving it just fine. And I know including Snarl is a stretch as you have to go out of your way to battle all trainers, but it's there so thought to mention it; not that it really helps as both Vikavolt and Togedemaru use a Physical moveset. Though I guess Snarl could be handy against Acerola, SPEAKING of whom.
Trial: Thrifty Megamart (Abandoned Site)(Route 14)
Captain / Type: Acerola / Ghost
Totem: Mimikyu
TM: Shadow Ball (on Route 14)
Some people may be disappointed that the Ghost-type Specialist is once again giving out Shadow Ball. These people are wrong and you should not listen to them because any advice they give would be bad. For Special Attackers that can learn it, which is quite a few, Shadow Ball is a godsend, especially since you can get it before taking on the Trial! Just remember, don't Z-Move before breaking Mimikyu's disguise, speaking from experience...
Trial: Vast Poni Canyon
Type: Dragon
Totem: Kommo-o
TM: Dragon Claw (found during Trial) and a few others scattered around (some notable being Dazzling Gleam, Wild Charge, & Flamethrower)
Being the last area of the game before the League, of course its NOW they're just dumping many good TMs on you, including the ONLY Fairy TM in the game! Well, at least you can make immediate use of it if you have a Pokemon that can learn it, and if not Dragon Claw may be more up your Pokemon's ally. And though they won't be useful here, Physical Electric-types would begrudgingly appreciate Wild Charge and Special Fire-types graciously appreciate Flamethrower. Just remember, don't Z-Move on the first turn because Kommo-o starts the battle with Protect. Speaking. From. Experience.
USUM BONUS:
Trial: Seafolk Village
Captain / Type: Mina / Fairy
Totem: Ribombee
TM: Flash Cannon
By the (awesome) Steelix Boat there's the Flash Cannon TM. Yeah, another stretch since it's also in SM, but eitherway if you got a Steel-type and/or Special Attacker that can learn it than give it Steelium Z and nuke the wannabe bee.