I like crossbows as a concept. There's just something about the loading and the aiming and the thunk. What I don't like as much are rapid-firing automatic crossbows or the kind of machinegunning that Crossbow Expert lets one do. Unfortunately (for me), 5E is built around martial classes doing two to four attacks per Attack action which just... doesn't worth with a Loading weapon.

That said, I'd like to make a character for who doing that one shot per turn is actually a viable use of their turn, rather than something you do when your preferred options ran out (for example, out of spell slots and your damaging cantrips don't work because of immunity/antimagic etc).

Ultimately, I'm looking for something similar to, say, a gish using one of the SCAG cantrips to attack once with their weapon of choice for good damage. And preferably not something that takes action+bonus action+concentration+spell slot to deal half the damage of a same level fireball.