If you wanted something that gets online earlier you should've said so :/

Vuman Fighter 1 / Valor Bard 10

At level 6 you have extra action, crossbow expert, 18 dexterity, and a handcrossbow. Result: 3d6+16. Not bad for a bard but

At level 11 you have swift quiver, extra action, crossbow expert, sharpshooter, 18 dexterity, and a heavy crossbow. Result: 4d10+16+40

At the start of combat, cast minor illusion to place a wall around yourself (when unseen, you have advantage on attacks - this works even if enemies are aware of your location, as long as they can't see you). As a bonus action, cast swift quiver. On consecutive turns you just sit in your illusory box and keep spamming four sharpshooter bolts per turn for some 60-100 ish damage (assuming 3 or 4 bolts hit).

After this you can either keep levelling bard for more high level spell slots (at level 11 you can use it twice per long rest) or level fighter for action surge and a martial archetype. Either way you want to get at least one ASI to max out your dexterity.