Well, here is my vr. I won't pretend I am an expert on the tier, but I think this is pretty good. Aside from D tier and obviously the Not Sure tier everything is ranked in order from left (best) to right (worst). Anyway, I would like to share my thoughts on certain pokemon I ranked.

I have never been a huge fan of Heatran in general (both competitively and casually) but this gen is probably its best gen besides gen 7. Despite that, I always thought it was a bit overrated. It is slow, 4 times weak to ground (one of the most common attacking types period), and I have always believed it is a pokemon you respect more on the teambuilder than in battle. However, I am not that good at the game, and I can also see the plentiful upsides of this pokemon such as its other stats, huge movepool, and its defensive qualities as a fire steel pokemon with a complete immunity to fire. Because of that I decided to put it in A+.

If it weren't for the fact that overheat hits slightly less targets than hydro pump and that Heatran exists, I would say both Rotom-Wash and Rotom-Heat are roughly the same level. Both can hit opposing pokemon absurdly hard with their form exclusive moves as well as their stab thunderbolt and shadow ball. They also both have excellent support movepools with moves such as trick, will o wisp, toxic and thunder wave (which aren't used that much but are still there), pain split, etc. They also have the obvious advantages of being ghost types and being electric types that are immune to ground. Overall, they are really good pokemon that are easy to fit and hard to find a reason to not use. On the other hand, there is Rotom-Fridge (I know that isn't the actual name it is just funnier) who has all the same perks as the top 2 Rotom forms but unfortunately has a worse exclusive move in blizzard which is far more inaccurate than hydro pump or overheat which makes it a higher liability. However, I do think it is still really solid as blizzard is an ice type move (which means boltbeam coverage) and with Abomasnow setting up hail, blizzard does become 100% accurate which is great so overall it is still a really solid Rotom form that isn't quite able to do as well as its Wash and Heat brethren. Rotom-Fan is dumb though. It probably doesn't deserve D tier and air slash isn't the worst move in the world but because of that one move it is far worse than its other forms in my opinion since air slash hits far less than any other Rotom form exclusive move. Finally, (as I don't know how to feel about Rotom-Mow) there is regular Rotom who has no exclusive moves and is thus likely unviable as it is outclassed by its other forms.

Nothing super important to say here. Just wanted to say choice specs Zapdos is pretty cool.

So, can someone please explain to me why everyone is ranking this pokemon so low? I know there are plenty of fire types and pokemon with fire type attacks that love to murder Scizor and that there are plenty of pokemon that resist bullet punch and u-turn but what really changed in the meta? Machamp getting banned didn't really increase the viability of most fire types (except Heatran) that much and if anything, many fire types got a bit worse because their attacks thud into Tyranitar and Heatran more often. I think Scizor still has plenty to offer with its powerful PRIORITY stab moves as well as its amazing bug steel typing.

This pokemon is weird to me because I kind of don't hear anything about it anymore. It's...a pokemon for sure. It has a great speed tier with ok attack and some solid movepool options, but it just doesn't seem that strong to me. Anyway, I am not a huge expert on this pokemon so I am going to stop talking about it and move on.

Without a doubt, Donphan is the second-best spinner in ou and the third-best in the entire gen (Forretress is actually good in ubers). Not only does it have insanely high defense which allows it to take at least one attack from almost every non boosted physical attacker in the tier but it also has some decent attack which allows it to take on Rotom and Gengar with assurance (which isn't the best move in the world but Forretress has nothing besides hidden power for ghost types so this isn't bad).

Machamp getting banned does give it a lot more targets to hit with steel types and Tyranitar becoming more common, but overall Lucario is unfortunately a bit mid which is a shame because I enjoy using it. It has some great priority moves but with the amount of pokemon that resist extreme speed and bullet punch in ou (there are 9 steel types in ou not including Lucario itself) it has a hard time taking kos sometimes. However, it is still a solid pokemon with a great movepool and good stats.

I think this is an underrated pokemon in many respects. Its stats are quite underwhelming, its typing has some pretty big weaknesses, and it is weak to stealth rock. However, it also has the unique role of being the ONLY POKEMON IN THE ENTIRE GENERATION (that isn't ubers, or a previous evo) that provides a weather effect on switch in that isn't sand. There are multiple advantages hail has over sand such as dealing damage to literally every type (except ice types and Clefable) in the entire game whereas before 3 types were immune to passive damage, as well as giving blizzard 100% accuracy which can be taken advantage of by quite a few pokemon in ou. Abomasnow itself also has some underrated resistances to electric ground water and grass which means it is great against pokemon like Starmie who don't have the coverage to threaten the ko on it. It also has some nice options in its movepool such as leech seed, ice shard, and even toxic. Abomasnow is a solid pokemon that I believe should be used/experimented with more.

This is another rather underrated pokemon in my opinion as despite its typing it does have a lot to offer. High defense, high attack, solid movepool, and an ability that makes me really wish Rhyperior was a pure ground type. It isn't the greatest pokemon out there and if you are looking for a specially defensive ground look elsewhere but Rhyperior is not bad by any means.

This pokemon probably isn't deserving of anything above D but I used it once on a mono water meme team and it did pretty well. It has volt absorb so it is immune to electric type moves and it has some good support moves like heal bell and toxic but it has pretty bad stats so it probably isn't worth trying to fit on a team.

Public service announcement: this pokemon sucks. NEXT!

And finally, I would like to give a special shoutout to Azumarill who is probably not viable but does have the combination of belly drum and huge power, so it has to count for something right? I am not good enough to actually test how good it is but it probably isn't.
Anyway, that is all of my thoughts on pokemon whose placement I believe might be questioned. If you have any other questions, please feel free to ask. Have a nice night :)