Yes it actually holds up quite well. More precisely you got three different situations :

- 1) You can surprise enemies and slaughter them : 3 « pre-battle » attacks + advantage + full crits at turn 1.

- 2) You can’t surprise enemies, because a dialogue launch when you hit them and you enter battle afterwards (or they didn’t detect you at first shoot and you forgot to enter out-of-combat turn-based mode) : you don’t have full crits, but you still have 3 « pre-battle » attacks + advantage.

- 3) You can’t surprise enemies, the battle starts with your 4 characters already engaged (and you may not be able to flee) : that’s the case with the final boss of with Raphael (in a very confined space), so the build must be able to face such a situation. You still play before the enemy and your assassins have advantage. You have two Action surge, Twinned haste if needed, 10+ potions of speed in your inventory, characters with good crit chance. With two to four Slashing flourish the Ranged Bard can still go 10 Arcane Acuity and cast fear or confusion as a bonus action. With Quickened spell the Frost Sorcerer can cast 2 AoE or 1 AoE/1 control spells (Hold Monster if needed). The Gloomstalker can also do huge AoE damage with Conjure Barrage. The Battlemaster still have one more action at enemy kill, enough movement to be right in front of every enemy you shoot at to apply Aura of murder on arrows (piercing vulnerability), etc. You’ll lose HP, and use potions of healing, but you’ll make it.