Suspect Tests always attract players who are foreign to the tier to play, and get a good feel of the meta, by playing countless games on the Suspect ladder and facing many different teams, playstyles, archetypes. All of these combined should craft a decent image of how the current NU meta is.
I feel that if these newer players want to get a feel of the meta, it's on them if they choose to do so in a suspect meta instead of the regular ladder. On regular ladder they can do all the experimentation they want with little consequence and face other such diverse teams, but in the dog-eat-dog world of the suspect ladder, success and efficiency are all that really matter, and you can't really fault Rain for that. If these newer players opt to begin exploring the NU meta
on the pretense of getting the TC badge instead of out of genuine interest (they would've probably first lurked the Neverused room instead of trying to experiment in the suspect meta) and have the 'misfortune' of repeatedly encountering Rain teams as a result, well that sucks for them I guess, but it's their decision.
Many people only play the NU Suspect ladder to get their beloved Tiering Contributor badge, and don't really care about the metagame at all. I completely understand that and there is no-one stopping you from this, but please don't create an entirely wrong image of the metagame by spamming Rain for 100 games straight if you don't know the tier. Getting reqs is an annoying task and rain makes it a lot easier for most people, but it gives people that are new to NU the idea: 'Oh, all I see on the ladder are staple Rain-teams and stall. What a boring tier this is. Let's stay away from this tier as long as possible after I get my reqs.'
On the other hand, there is no guarantee that those same players who visit the NU meta purely to get reqs for their TC badge would really stick around even if the suspect meta didn't present itself as 'Rain-heavy'. Also, are you referring to the Rain spammers creating this image for themselves (since you highlighted 'if you don't know this tier'), or creating this image for newer players? Because if it is the former, there isn't really anything wrong with that since that is just their own opinion. As for the newer players, I've already mentioned that it's up to them whether they choose to explore the NU meta on suspect meta or regular ladder, and once again, it's not really Rain's fault.
I get the message you're tying to convey, but I just want to address some of your arguments.
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Now for the elephant in the room:
Sawk has been a part of the NU meta since the very beginning, and while it certainly wasn't too problematic back then, several things have happened for it to achieve the dominance it has today. The departure of several fellow threats, as well as its checks such as Doublade, Qwilfish, Spiritomb, and others, have allowed Sawk to inch its way up the hierarchy, but the likely tipping point is around the release of ORAS, where it received Zen Headbutt as a tutored move. With this move, Sawk now attains utterly flawless Fighting / Dark / Psychic / Rock coverage. The departure of Granbull didn't help matters, as Choice Band Sawk now threatens a 2HKO at worst on pretty much everything bar Colbur Musharna and Colbur Gourgeist-Super, and when your sole counters require resist berries just to keep you under proper control, you're on pretty shaky ground as is.
Of course, there are several other factors to Sawk's suspect status. Its raw strength and perfect coverage are tough enough to deal with, but Sawk happens to sit in an above average Speed tier (ahead of other premier hard-hitters like Shiftry, Magmortar, and Kabutops, neither of which hit as hard as Sawk does btw), and basically defines the Speed tier for wallbreakers. Sawk is almost guaranteed to outspeed at least two members of a team even if it is built offensively, but Sawk is far from helpless against faster opponents thank to Sturdy, most of them it can OHKO, so an unharmed well-played Sawk is extremely difficult to deal with without suffering huge casualties. Sawk's presence has been clear in this current meta: Xatus are practically forced to run the same 252 HP / 176 Speed Timid spreads with Colbur Berry or fail to consistenly check Sawk, and of course the fact that Colbur Berry has become a standard on most Ghosts and Psychics (especially the aforementioned Gourgeist-Super and Musharna) when they could otherwise consider other items is a testament to Sawk's power. It doesn't help that Sawk's two best counters are rather exploitable, especially with a Snow Warning teammate.
Even if Sawk's primary favorable matchup is against slower teams, Choice Scarf Sawk has proven to be a strong alternative threat, especially in the previous suspect meta. As it turns out, cleaning games with Scarf Close Combat can be pretty easy when Sawk's coverage moves in Knock Off, Mold Breaker Earthquake, and Stone Edge are also fairly comfortable choices to lock Sawk into, especially with that kind of power backing them up. It shows that Sawk does not falter even in a faster metagame that attempts to curb the presence of Sawk with its natural Speed. Speaking of Sawk's other sets, Sawk can make use of Expert Belt or Black Belt to bluff sets and take advantage of opponents who rely on Sawk to be Choice-locked to counter it, which is a lot of them. Hell, Sawk can even make use of Taunt to best one of its hard counters in Gourgeist-Super while tripping up some of its other checks.
With that said, these are thoughts I've had about Sawk when it is present in the meta, and from my experiences in the Sawk-less meta, I might just have to say...
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...that people have been a bit
pampered by Sawk.
The other Fighting-types in Hitmonchan, (offensive) Hariyama, Primeape, etc. are somewhat capable of filling the void left by Sawk, except be a bit less, you know,
ridiculous at it. Sawk may have been blessed with its flawless coverage and even its offensive stat distribution, but it's not like the other Fighting-types "scrape by"; they still have the potential to threaten enough of the meta, while possessing adequate coverage to cover a large majority of would-be checks, just not practically all of them like Sawk does. Now people may actually consider their teambuilding issues and/or what tech moves to put on their Fighting-types instead of just resorting to Sawk's picture-perfect coverage and stats; there's a difference between banning a threat with respectable coverage and be left with alternatives with poor / limited coverage and offensive potential, and banning a threat with flawless coverage and be left with options that still have workable coverage and offensive prowess, and Sawk's case definitely feels like the latter. I believe Sawk has been the 'role model Fighting-type' for a tad too long in this meta, and other Fighting-types should have a better chance to shine and be considered more on teams.
Tl;dr: I would likely be in favor of banning Sawk, slightly on the grounds of it being OP, and more on the grounds of its departure leading to a more diversified meta.