Note: I tend to skip every trainer I run into unless if
a)It's mandatory
b)It hides an important item, like a rare candy
c)My party feels clearly underleveled (usually only happens in the late game or in very specific sections)
So I will likely have a different experience with some mons, as they will be relatively underleveled compared to the other playthoughs in this thread, (I tend to use parties of 4 Pokemon though, which is considered the standard in this thread). For exemple, in Squitle playthroughs I fight Brock at level 8 (last trainer in Viridian only), while with Bulbasaur I fight him at level 12 (Leech Seed + Tackle takes too long otherwise, from what I tested, and this way you get Vine Whip mid-fight). I pretty much do what I would consider "more efficient" depending on the situation
On the topic of Bulbasaur, B tier is clearly underselling it. It performs really well against the first 2 gyms and does fine agains the 3rd. Now, I 100% agree that relying on Cut/Body Slam until you get Razor Leaf sucks, even more so with Vine Whip's limited pp... However, once Ivysaur gets Razor Leaf at level 30 it can clean up trainers and boss fights really easily. With Gen 1 crit mechanics Razor Leaf will crit 240/256 times as Ivysaur and 255/256 as Venusaur, which means it effectively has 55*1.5(STAB)*2(Crit) = 165 power, basically a Z-move. It straight up 1 hit kos weak and even middle of the pack pokemon, as well as 2hkoing everything that doesn't resist it, even the higher leveled enemies.
Also, toxic+leech seed (they multiply each other thanks to a bug in this gen, as I'm sure we all know), while slower than just simply going for Razor Leaf (takes 3-4 turns, as opposed to 1-2), is a pretty legitimate way of getting past non-poison type pokemon that resist Razor Leaf. For instance, I just tested and beat Blaine, the fire type gym, with 0 issues, ending the fight at full health. Now, this isn't something you would do in a normal run, since by this point of the game you should have a better pokemon for this fight (as in something that can beat it in 4 turns instead of like 12-16), but it highlights how, even in problematic matchups, Toxic+Leech Seed is a valid strategy. Though I can see the value of Swords Dance+Body Slam to get past poison types, obviously.
C Tier
-Tentacool should not be this low. You can catch a level 40 Tentacruel by using a repel, which is 10 levels higher than its late-game water type competition (like Staryu, who is A tier). It has the highest special stat of any water type and has good means of getting past other water types with Mega Drain (a tm that is in low demand), something most water types lack (like Vaporeon). It's also quite fast and will out speed almost everything.
B Tier
-Duduo, Farfetch'd and Spearow in the same tier seems really weird. Duduo is far better than the other birds, it's not even close. I tested spearow recently and its bulk is really poor and detrimental early game, especially in the rival fight in Cerulean. Meanwhile its power is nothing special, and it seemed like it was stealing away experience from my Bulbasaur, if anything (I retested that starting part of the game with only bulbasaur and it went far smoother). Mid game it's stuck with Fury Attack and Peck until it finally gets Fly, while Farfetch'd can be taught Body Slam (a tm in high demand yes, but it allows it to be immediately useful, even though it will be slightly under-leveled at first) and has boosted exp as well (not to mention the unique Cut+Fly combination). Farfetch'd on the other hand is worse than Duduo, being extremely reliant on the Body Slam tm to perform, and its stats really start to show late-game. They should probably be ranked A, B and C tier respectively, in my opinion. I can also see Duduo and Farfetch'd in the same tier, which would lead to 2 B tiers and a C I suppose.
Omanyte being in the same tier as Spearow, despite being one of the best water types available, seems really inaccurate to me as well, which further makes me think that spearow needs to be lower.
A Tier
Kadabra should be S. It's a complete monster and the only tms it even "wants" are Seismic Toss (extremely low demand) and maybe Thunder Wave for some cheese (for Sabrina, mostly, maybe Misty as well). I would like to mention that obtaining a Kadabra before Misty is really easy (it will evolve on the way to Bill's house) and it has by far one of the best matchups against it (Seismic Toss 3HKos at level 20). If anything, Alakazam should be S+ or something, since it's clearly the best pokemon in the game, by a pretty decent margin, even moreso with the added restrictions.
Squitle seems fine in A since X accuracy is banned, which weakens its Elite 4 matchups a lot.
Magikarp is such a massive experience sink. Does it really deserve A? It's super out of place, being in the same tier as Squirtle and Staryu.
I think the old list might have had the right idea splitting Bulbasaur in Y and RB, but I might need to retest Yellow Bulbasaur to know.
Diglett not being S seems insane to me. A single repel lets you catch a Dugtrio in about a minute and it comes at level 29 at worst, which is super over-leveled by that point. It also auto-wins against the gym leader right next to it. With Dig being 100 base power and Slash auto-critting, it smashes just about everything it runs into. Rockslide tm is just a cherry on top. I think "late-game problems" are being overstated.
S
Snorlax in A seems high to me, let alone S. It's super slow and drags fights for much longer than any of the S and A tiers.
I don't think I've ever used Jynx, but I will definitely test it soon.
Finally, I really don't think One Hit Ko moves with X-Accuracy would centralize the list as much as suggested. All it would do is bump Pokemon like Squirtle (S tier) and trade Seel up. Pokemon like Nidoking deserve S-tier regardless. This combined with them being an obvious, even if silly mechanic (using something that increases accuracy to make an inaccurate move hit), makes me think they are 100% legitimate for a list of this kind. Banning the use of X-Items is creating artificial restrictions, and this type of interaction is very different than something like the missigno or the mew glitch, which require you to do arbitrary things you would only know how to do with a tutorial and are clearly glitches. Now, using a team of around 4 pokemon is also a self-imposed restriction, but it makes sense, since otherwise you end up with 5 early game pokemon in the upper tiers and everything else in the worthless tier, which would be pointless. But obviously most people seem to disagree with this and this is not my thread, which is perfectly fine and I respect it.