Where are Gastly (sprout tower night), Tauros, and Miltank in GSC?
You can get Tauros/Miltank (and Stantler) right after Sudowoodo and they're level 13-15 and have superior stats to damn near everything.
Cyndaquil is a massive pain to train from what I recall, but once Typh gets Flamethrower, game over foes!
Bellsprout is awful in GSC. Even if you catch one at sprout tower it sucks unless you chose Cyndaquil. Yeah, you can level up in Union Cave... and then get your hide varnished by Bugsy, Whitney, Morty, Jasmine, Pryce, and Clair. Bellsprout is like a worse Chikorita whose only saving grace is Sleep Powder.
Zubat is a mixed case. On the one hand it needs a LOT of babying. On the other hand, if you don't let it faint too much and take it to the hairstylist you'll have a Crobat by Level 40 that can hit anything with Confuse Ray and then Wing Attack it to death.
Remoraid was tough to catch and you had to wait a while if you wanted a swarm, but you could always powerlevel to 44 to get Ice Beam and then rape everything with Octy.