Alright, here to post my takes on the RBY OU Viability Ranking. Note that these are ordered within tiers. I have some takes hotter than a bag of steamed broccoli straight from the microwave, so get ready. I'll try to explain them as thoroughly as possible. I won't be going too in-depth on the standard opinions however. Sorry there aren't any nice visuals, doing that on phone is annoying. There may also be occasional grammar issues, for the same reason. Feel free to ask me about anything, I love discussions about RBY!
Alright so right off the bat, Chansey at the #1 slot is a pretty big one. While yes, there is that one quirky VicNite team that drops it, I don't think that's enough to argue it as that more droppable than any of the other Big 3 Normals, the primary reason people put it as #3. Nearly every team WILL feature it, so I put them around the same level.
Now, as for why the order is the way it is.
Tauros relies on Snorlax and Chansey to reach scenarios where it is able to perform effectively, as they are responsible for manipulating the midgame to create an endgame scenario that allows Tauros to thrive. For this reason, I put it at #3.
Snorlax vs Chansey is a hard one. However, due to Pokemon like Cloyster, as well as the funny duck Porygon, it can find itself struggling in certain matchups. Another issue is that Gengar's increased usage can force it to run Earthquake, which restricts its flexibility that causes it to be so good.
Chansey on the otherhand is just so damn flexible. It compresses so many roles nicely, has a movepool to accomplish nearly any supportive role, and is just one dense motherfucker. It also has the advantage of causing its checks in Physical Attackers trouble at times due to Counter and Thunder Wave. Personally, any order of the Big 3 is fine, but I stand by this opinion.
Moving on to the next tier, it comprises itself of the 3 Big Dick Psychics. Not that much to say here since the takes are common. Alakazam over Exeggutor has some discussion, but personally I'm not a fan. Exeggutor is the best sleeper in the tier, while Alakazam is not the best fast Psychic that spreads Paralysis. Exeggutor just also does more shit than Alakazam as a role compression machine and a Boomer. You'll find a general trend in my VRs that I value pokemon with good Role Compression more highly than a good pokemon that's narrow.
B+ is a bit interesting. The two mons selected in Rhydon and Zapdos are pretty typical, but the ordering between the two flip based on who you ask. While Zapdos is really good, it has a few poor matchups (especially Rhydon teams) that cause it to be a bit more matchup fishy than Rhydon. It also has to compete as an Electric-type with Jolteon, while Rhydon's only competition is the fucking ball of Rock in Golem.
B has one of my hotter takes in Jynx #10 below a Cloyster #9. While Jynx is a great sleeper, it doesn't really do anything else that other Pokemon can't also do. You click Lovely Kiss, maybe fire off a Blizzard or 2, and then just kinda roam around the rest of the game like an ADHD Kid in an Arcade.
Cloyster on the other hand is able to do more. Its also a freeze fisher, but it also acts as a Snorlax check and an Explosion user, and it has pivoting abilities in Clamp. It just has more use overall, leading to me placing it #9. Jolteon is very close behind the 2 at #11, and everyone knows why it works. Fast af, STAB Electric, Thunder Wave, Double Kick + Pin Missile, Zapdos check, the works.
Gengar is here as well. While I value that its a sleeper with some defensive capabilities due to its Ghost-typing, it's partial Poison-typing really holds it back. Tauros Earthquakes and Mie/Dam can be a pain in the arse. It definitely works, but its weaknesses put it a step below Jynx Jolteon and Cloyster imo.
B- is kind of the borderline here. These should be OU in my opinion, but they are definitely less of a mainstay than everything before them.
Slowbro is an absolute mammoth when it works, but much of time it kinda falls flat due to its inherent inconsistency as a slow setup sweeper which requires multiple consecutive opportunities to setup. The excellent typing and access to Thudner Wave definitely keep it viable though, and in my opinion acts as a kind of borderline between the common OU threats and the niche ones.
Lapras has seen better days, but it is able to pack in enough important roles to stay afloat as an OU Pokemon. Articuno would be UU by this nomination, and my reasoning for it is on par with Plague von Karma's earlier post.
Time for the C rank! Immediately we have one of the juciest takes in Porygon > Victreebel. If this was a Youtube thumbnail there'd be at least 7 red circles and 4 red arrows surrounding these two.
Victreebel has seen better days, and everyone knows it. It's primary use is moot when most players don't use slow teams anymore, and it is just rather inconsistent. Most people would agree that its no longer truly an OU threat, like it still works but its not on the same level as other shit.
Porygon on the other hand does nothing but counters Snorlax sets besides AmneLax. However, it accomplishes this extremely well and does it very consistently, which puts it above Victreebel in my books.
After this everything is quite standard. I left out some common E rank choices because I just truly don't like them at all, notably Machamp, Flareon, and Clefable. I just never really find much reason to use them, but in general the E Ranks come from maybe a couple uses each. Only other thing that's unique is that I rank Golem low, mainly because in most situations where you'd use it, just use BoomLax and/or Rhydon tbh.
That's my Viability Rankings! I know some of these may be contested by different people, but I hope they at least made sense.