It's not a race where turtle & the hare style slow & steady vrs fast & intermittent averages out in meaningful ways . Hitrates in o5e are usually around 60% or better so there is no reason to fractionalize the attacks that do hit
- Even if the hitrate drops significantly due to an unusual high ac monster it still favors the numbers still favor the higher damage attack because the smaller but reliable attacker is also affected by that AC & in this case the attacker with the higher damage attacks also has more chances (one Xd10 firebolt vrs X[1d8+statmod+weaponmod+featmods+fighting style mods] attacks) in a true inversion of the tortoise & the hare type of averaging you are doing.
You're not claiming that a melee focused fighter will ALSO have a ranged fighting style, ranged feats for support AND as good a weapon as he uses for melee, are you? Because that's really, really unlikely.
Or are you saying the fighter will get to use his melee skills soon enough and that has to factor? That's much better, but the wizard has cool things he can do outside of firebolt too!
But let's talk about the actual point I've been making since early in the thread. Even if you concede that fighters are fine, even excel in combat (which I actually did early on just for convenience):
1. The other classes excel too, maybe in different ways, but no class is a slouch in combat. The game is designed that way.
2. They get very, very little support out of combat for the other 2 pillars. And the support they can get (feats, ASIs etc.) is often sacrificed so they can be the beast in combat everyone expects them to be. And IMO - that's an issue.