Incidentally, if you are willing to give up "crit fishing", Smite is exactly one of those abilities that would MOSTLY work just fine as a direct-use ability (like Battlemaster superiority dice maneuvers already do) except for when it's applied on top of a AoO as a reaction (THEN it would need a prompt).
And yes, GM4Him nailed what I meant with "virtually no interruptions". If you are paying attention to the action and expecting the reaction to come by, as soon as the "dramatic slow down" is even beginning you'd be quickly able to left click to confirm your reaction or right click to skip it. Then the action would go by with hardly any actual pause. And even some eye candy on top, if you like that sort of thing.
If anything, a compromise I could see is that when a "spell slot use" is required (i.e. Smite), the game could set for a compromise (i.e. "Always use the lower -or higher- level spell slot available instead asking which).