Flamestrike
Legend
The problem with it, even when you do set it up, is simple math:
Just a typical situation off the top of my head, you may get a 60% chance to hide, 84% chance to hit (advantage accounted for), 60% chance to win initiative:
An Assasin will have expertise to Stealth, and presuming feats, have Alert by 4th level (granting a +8-9 to initiative), and +9 or so to Stealth).
It's the set-up that is the harder part.