Gloom Stalker / Assassin: sick multiclass?

[Guest 6801328]

The saving throw requirement is the biggest problem. The value of a devastating alpha strike is to wreck the big boss monster at the start of combat... and big boss monsters are apt to be legendary, especially at 17th level, which means they can shut you down hard. Plus, it's a Con save, which high-level boss monsters are generally quite good at.

But even setting that aside, you actually don't gain much. Let's try a 17th-level gloom stalker build: Ranger 5, fighter 2, rogue 10. Using Action Surge:

First attack: 1d8 (base) + 1d8 (Dread Ambush) + 1d6 (hunter's mark) + 5 (Dex) = 2d8+1d6+5
Second attack: 1d8 (base) + 1d6 (hunter's mark) + 5 (Dex) = 1d8+1d6+5
Third attack: 1d8 (base) + 1d6 (hunter's mark) + 5 (Dex) = 1d8+1d6+5
Fourth attack: 1d8 (base) + 1d8 (Dread Ambush) + 1d6 (hunter's mark) + 5 (Dex) = 2d8+1d6+5
Fifth attack: 1d8 (base) + 1d6 (hunter's mark) + 5 (Dex) = 1d8+1d6+5
Sixth attack: 1d8 (base) + 1d6 (hunter's mark) + 5 (Dex) = 1d8+1d6+5
Sneak attack 1/turn: 5d6

Total: 8d8+11d6+30
Doubling all dice from automatic crits: 16d8+22d6+30 (average 179)

The assassin, meanwhile, gets 2d6 (dual shortswords) + 11d6 (Sneak Attack) + 5 (Dex). Doubling all dice from autocrits, that's 26d6+5, averaging 96. Doubling that is 192 average damage, a mere 7% gain. And it doesn't come online until 17th level, where the gloom stalker has been wrecking bosses since level 8.

Of course, this is assuming all attacks hit and the target fails its Con save; I haven't yet run the math on how those failure chances affect the total, but I think it favors the gloom stalker.

On the other hand, the Fighter mix can do that once per rest. The Gloomstalker/Assassin or Assassin can do it all day long. (The Monk blend is limited by Ki, but can still pull off quite a few alpha strikes.)