Sharpshooter is garbage? Please. You are obviously saying that just for the sake of having a counterargument.

Aiming carefully and popping off heads is the greatest enjoyment possible in a shooter game.

Proof: the popularity of shooter games such as Call of Duty, Counter-Strike, and Battlefield dominating game sales.

You don't see entire genres built around spamming fire, do you? That's because there's nothing to learn, nothing to improve on, and nothing to feel a sense of achievement about.

As for your point about Firebug being somehow "fun", I say this:

Godmode is fun, should that be enabled by default in the game too? What about infinite ammo? What about flying?

This is a co-op game. There's a balance between what's fun and what's not fun to keep the game enjoyable for everyone.

And "Firebug has other weapons"? Oh, this argument again. What does it matter, when 99.99% of Firebugs always go for the Flamethrower because it's the easiest to use and will allow them to hoard the most kills?

There could be a Firebug Sniper Rifle, for all I care. Is it going to make one bit of difference when the vast majority of Firebugs always go for the Flamethrower instead? No, it is not.

We can argue about this all day, pal. You're not going to win.