Have people been crunching the dpr numbers? I have been considering playing a high dpr archer as a change of pace from my utility casters.
Just off the top of my head:
-battle master with sharpshooter and crossbow expert (maneuver damage + bonus action attack)
This is a straightforward path to great overall performance. In fact, it's probably so good it breaks the entire game (why go melee when you can do this?!)
Essentially, this turns your crossbow archer into a melee character with 120 ft reach!
And not only that, you get the same übercrazy damage potential as a greatweapon wielder! Sure you don't have a d12 damage die, but who cares when you never waste an attack for want of an eligible target.
Don't use your battlemaster maneuvers for extra damage, though. You'd be better off using Precision Attack (to turn misses into hits), enabling you to use the Sharpshooter -5/+10 part on scarily high ACs.
Since you obviously will attack monsters set up so you have advantage, you should find that even with the -5 from Sharpshooter, you will nearly always hit when you need to roll around 10 on the d20. (the 50% miss chance first shrinks to 25% from advantage, then to 15% from, say Guidance, then into low-single digit numbers if you apply Precision Attack judiciously. If you also have Lucky, you could go entire days without missing a single shot. And that, ladies and gentlemen, is true power! (In fact, we're looking at 4d6+60 damage each round...

)
(Sharpshooter is so broken it isn't even funny, but I must admit it is kind of hilarious to read about those poor saps flailing about trying to deny it)
I'm more concerned about mid levels, I'll never see the fighter's 4th attack.
Forget about the fighter's 4th extra attack.

You get four attacks
already at 11th level (since you're effectively dualwielding here - making a bonus action attack every round)
In fact, that's not the end of it. You can gain a fourth attack
already at level 8! (Fighter 5 for two attacks, Crossbow Expert for bonus action attack, and Ranger 3 for Hordebreaker - encountering adjacent enemies is very common). Obviously Fighter 6/Ranger 4 is probably a more realistic target, since it's two more ASIs, but still - faster than Fighter 11!
This means you'll commonly do
five attacks at level 15, if that's included in your "mid-levels".
Six if you set up a reliable way of making opportunity attacks. (Not saying this is actually worth it, but War Caster enables you to make your opportunity attack using a cantrip, which nicely scales even with you not having any spellcasting levels. But a feat that lets you make a 3d10 opportunity attack even with no melee weapon in hand is nothing to sneeze at...)
I haven't more than casually browsed the UA subclasses, but I have not seen anything worth a powergamer's time. (I would love if I was educated otherwise) The build above is pure PHB.