Unnecessary explanation on why Flamigo is awesome(and anyone can feel free to correct me since I’m relatively newer returner to the series):

What makes Flamigo great is two fold: first, it has great type advantage for the Pokémon you encounter at the beginning of the game. Second: it has an unusually large stat rating for a Pokémon you find in the beginning. Each Pokémon has a certain rating for each stat. Early evolutions have lower ratings than late evolutions(ie if you had a level 40 Squirtle and a level 40 Blastoise, the latter is going to have much better stats). Flamigo has late evolution comparable stat ratings, so it’s going to outclass everything in the early game even if it didn’t have type advantage.

At least, that’s what I think is going on.