Am I the only one who has noticed that we actually have 2 entries for RB Bulbasaur in the list of the OP, one in Top tier and one in High? That should probably be fixed lol
I'm just updating with my thoughts on Tangela and Kabuto (and the others).
Tangela sucks. Not that I needed to do a playthrough to know this, but it just isn't good for the purposes of efficiency. It has good stats but its terrible movepool (probably the worst of all the grass-types) cancels this out to make battles drag on and on and on. It doesn't do that well against Erika, or Koga, or Sabrina, or Blaine, or Agatha, or Lance, or much at all really. This is Low as hell.
Kabuto is actually pretty good. You do have to deviate from what many would consider the "normal" pathway for a playthrough to get it early, and it starts off a bit slowly (especially compared to Omanyte), but this thing catches up quite quickly. It is so convenient that Pokemon Mansion seems to be designed specifically for grinding all of the other fossils. It gets Slash at level 39 and evolves 1 level later, and its Special is good enough to use Surf as a secondary attack. It made short work of Sabrina with Slash and it can beat Blaine and Giovanni, so it has some good match-ups. Seems like an interesting candidate for Mid at the moment.
Chansey and Kangaskhan... will probably get Low. They are both really good pokemon for different reasons, but they usually take ages to get and the time you save by using them is more than cancelled out by the time you take to find them most of the time. Sure, if you just happen to find and catch one as you are going through for the Surf HM/Gold Teeth, then use them and they will be awesome. But I really don't like the idea of actually RECOMMENDING them when planning a team since looking for them will probably waste a lot of time. No matter how good they are, there are many alternatives that can contribute just as much to a playthrough but are easier to obtain. For this reason, I think Tauros should get Low as well, though I probably won't write up Tauros.
I still don't like Slowpoke. It is so slow and weak as a Slowpoke and even as a Slowbro it isn't powerful enough to get away with being to sluggish (unlike, say, Snorlax). 75 Attack and 80 Special might have been ok if it could actually outspeed things, but it doesn't so it isn't. It often can't OHKO opponents which means it takes 2 hits before KOing the opponent. Good thing I have Softboiled Chansey. On the other hand it has a good movepool and great coverage for some important battles and it is fairly bulky after it evolves, although it evolves a bit later than I'd like. So I don't know what tier to put this in yet. I'm inclined to say Low though.
Growlithe could actually be High. I originally thought Mid but I have been using this for most of the game and it is so powerful as long as you evolve it as soon as possible. It's like a Charizard in the way it plows through everything, except that Dig hits even harder. It lacks Slash, but it has alternatives that hit pretty hard anyway. I guess its reliance on Dig and the fact that it comes later than Charizard are the main arguments against it though.