Disclaimer before I get to the rest of the post: This post is mostly about things that i have seen from olt as my evidence as why i think these changes should happen
Mega Latias: B+ --> A-
This thing saw a bunch of usage in olt. Its calm mind sets are amazing, but so are its reflect type sets to make ttar less of a check. It also has roost three attacks and roost defog two attacks sets that are amazing. It is also a huge counter to zard y duggy teams without ttar, and if they don't have ttar lati can just set up in their face and win. Also, with toxapex and other fat things that lati can set up on being so prevalent like mew, it only makes mega lati better. It is also in this team which was arguably the most popular team in this cycle of olt:
http://pokepast.es/5d3e7c37a87e939c
Clefable: A --> A+
This one i can see if it doesn't go through, but I do believe clefable does deserve a spot in A+. For a while now, but especially olt, this has been one of the most splashable mons on literally any team. With balance being as good as it is, being a great bulky stealth rocker or/and a bulky calm mind sweeper is fantastic. It can also run knock off, thunder wave, and even toxic to help its matchup against other teams. In olt it saw a bunch of usage, specifically on these teams:
http://pokepast.es/5fc205c0be960e50 http://pokepast.es/5d3e7c37a87e939c and the semi stall team used in olt a lot with the ditto, chansey, skarmory, zygarde, and medicham. And, it is also, as always, amazing on every single stall which is one of the best playstyles this gen. Overall, clefable is a monster.
Mega Scizor: A- --> A
Obviously, mega scizor was amazing early on in the gen with megagross being broken, but after it was banned scizor dropped down a lot in usage and viability. The SD roost knock off bullet punch set is amazing right now, as it invalidates aurora veil, and has knock off to pressure celesteela and toxapex so that they aren't super reliable switches/if needed scizor can risk scald burns vs toxapex and set up right in its face if it for some reason doesn't have haze. It also has bulky defog sets to be a super reliable defogger, especially on the double defog balance with mantine, tapu lele, weavile etc. It also saw great usage in this team during olt:
http://pokepast.es/5fc205c0be960e50 as well as the other one used in olt with kyurem black, weavile, heatran, tapu fini, and landorus.
Mega Venusaur: A- --> A
Mega Venusaur was one of the very most used pokemon in olt this cycle, and probably a top 3 most used mega for olt as well. Being a soft check for ash gren before it evolves, a check for zygarde, a dugtrio answer, tapu bulu check, mew check, toxapex check, mega diancie check, ferrothorn check most of the time, a check to non cm stored power clef sometimes, etc. It is just such a great defensive mon and pairs greatly with celesteela and toxapex, two of the other most popular mons right now. It was used in teams a bunch in olt like balances with celesteela, toxapex, reunuclis, etc. This hit a huge spike up in popularity and for good reason.
Zapdos: A- --> A
I think this one is long overdue. Zapdos fits on so many teams with so many different sets and so many utilizations. It is amazing on balance, it is a great celesteela answer, it is really good against stall, it has the offensive agility set, it has roost three attacks, it has roost defog two attacks, and even if you want you could possibly run u turn or volt switch to catch people off guard and get momentum. It is also amazing on rain with agility and z move. It was also used in this team that was very popular in olt
http://pokepast.es/5fc205c0be960e50
Mega Lopunny: B+ --> A- (possibly even A)
Lopunny got a lot of usage in olt and world cup. It has a lot of variety to fill a bunch of different roles. It can run ice punch, return and hjk are a given, power up punch, fake out, quick attack, toxic, copycat for spikes, tspikes, rocks, webs, and even healing wish to help a teammate. It is a great cleaner with amazing speed, it can be a sweeper when things are weakened, it can be amazing on hyper offense or bulky offense with spikes support which is very easy to fit this gen with gren, ferrothorn, skarmory, etc. It was also used in the team during olt with zygarde, clefable, magearna, lando-t, and gren.
Dragonite: B- --> B
I love dragonite, so I might be biased, but i think with the great popularity of the birdspam team, this is a valid rise. There really is not too much to say about this. Dragonite is on a really super popular team, and he's kind of just a set up and sweep pokemon. The problem with dragonite is that it actually does suffer from 4mss. If it had more than four moves, it could literally beat every pokemon after one or two dragon dances, but it can't do that because it doesn't have enough moves. But, it still can choose what pokemon it wants to counter essentially, making it a great addition to teams that are weak to a certain pokemon. It also does have a great bulky dragon dance roost set with leftovers, a choice band set, and even a really niche expert belt special attacking set which isn't really known or used but it can be good for taking on landorus', tangrowths, magearna, etc.
Gliscor: C -->B-
Gliscor saw virtually no usage this whole gen, until this cycle of olt, where it really shined. It was used on the mega latias team that I showed earlier but if you didn't wanna see that, the team is right here
http://pokepast.es/5d3e7c37a87e939c it really shines against stall where it can set up on virtually anything on stall and win, due to the fact that it can't get statused or trapped by dugtrio, and weavile isn't on stall at all anymore. It is also really good at annoying bulky teams, so overall I think it is well deserving of a rise.
Tapu Koko: A --> A+
Everyone explained why this should move up and I just wanna say that I agree with everything that everybody else said for why this should rise.