Ok a lot of these are biased, opinion based or apply to chimchar as well. Infernape can learn Grassknot Killing swampert, whiscash and hippowdon pretty easily, a Swords danced close combat can kill almost anything, even a 252 hp /252 def bold vaporeon has an incredibly high chance of being OHKO'd by a +2 CC with stealth rock damage , so in game it's more than enough to take out whatever you need it to.
Now while Empoleon is a great pokemon, he doesn't become as useful as Chimchar/turtwig do until he gets surf, which is a ways away from the start of the game.
Infernape learns Thunder punch and earthquake so along with his STAB attacks ( fire and fighting ) he can easily take out every gym in the game given you take the time to stop by a movetutor to teach him thunder punch >
I don't even like Chimchar/Infernape.