Butterfree C-
+ Available just at the start of the game.
+ Very quick evolution (10 lv)
+ Nice statistics for beginning (90 SpA, 80 SpD)
+ Quite nice movepool: Presence of powders, silver wind and bugg buzz on relatively early stage of game.
+ Tinded Leans are pretty nice
- Statistics nice for the beggining are dissapointing on next stages of game: 50 Def and 70 Speed, what make difficulties to survive next attacks
- 4x weakness to rock and 4 more 2x
- Do not resist clash with its class rivals. Is generally too weak.
Also i have some objections about:
Arcanine - There is not mentioned that Fire dog can learn Extremespeed - Powerful +2 piority move.
Venusaur - After Chapter 17 Bulbasaur doesn't learn Leech Seed at 7 lvl. He must be learned by move relearner, which is accesable on rather late point of game. It is a shame because it is his signature move i guess and lack of it limites his potential.
Swoobat - Endeavor with his speed is a quite powerful technique. That move, combined with Arcanine's Extremespeed have helped a lot dealing with Amaria.