Some pokemon types feel so unnecessary in red and blue. I think bug and poison type should have just all been grass type. Bugs and grass are both weak to fire. Poison kills grass but all grass types are part poison so it does nothing. Bugs are supposed to be strong against psychic, but ghosts could have done that. Adding poison type to ghosts ended up making them weak to psychic. Adding poison to grass types makes them weak to ground, but a grass type is what you would use against a ground type.
Not all Grass types are part Poison! Tangela was pure Grass.
But… yeah, the type balancing was the least of Gen 1′s problems, honestly.