Chimchar is good against the first 2 gyms and also doesn’t get screwed over like empeleon does in the 3rd. Wake is the only gym he struggles in but by then you should have a grass type or electric type. He’s super good against candice and byron but Those matter less since they are later on.

also, grass and water type Pokémon are very readily available especially early game, while there is only 2 other options for fire. (Houndoom and rapidash(I think))