I have used a Low Kick Mankey in Yellow to beat Brock several times recently and it swept him easily every time without any support. So yes, I can say from experience that it DOES man-handle him alone just fine, thank you very much.
Anyway, I decided to go through the tier list again to see if I could spot anything that seemed odd. For the most part (disregarding stuff like Growlithe at the moment which have already been brought up and will probably be changed at some point anyway) I think the list is good, but I have 2 things to say.
Warning: I'm about to contradict stuff I've said in the past by bringing these up, so bear with me.
Firstly, I'm wondering if Spearow should be bumped up to High again. I made arguments before to put Spearow in Mid and I stand by everything I said about it back then, but I was specifically talking about the Spearow caught near the start of the game. One thing I think I overlooked is that you can catch Spearow west of Celadon City, along with Doduo (Fearow can be caught in Yellow too, although it is rare and Spearow evolves soon after catching it so it isn't worth looking for it). Now, we have put Doduo in High, and given that Spearow can be caught under the same circumstances, I'm not really sure about whether Spearow should be below Doduo. If we wanted to compare them, I guess it comes down to evolving earlier (Fearow) vs. having more power, slightly earlier Drill Peck and Tri Attack (Dodrio) and I would probably just use Doduo, but ignoring this comparison, would a Spearow caught west of Celadon for the purpose of beating Erika be good enough for High? It probably serves the same purpose as Dodrio overall even if it is inferior to it.
Secondly, I think we should separate Yellow Psyduck from RB Psyduck, and put Yellow Psyduck in Low. I did say before that it wasn't worth the time to separate them, but that was when we were being conservative about splitting entries by version (I think the starters and Machop/trade Machamp were the only ones with separate entries at the time). Since we have now done it for Growlithe, Farfetch'd and Krabby, we might as well do it for Psyduck as well. I mean, it's so underleveled in Yellow...