Arguably, anything 'bleak' in the MCU was *earned* over a period of many films and years in real-time, i.e. a natural consequence of the storylines and their logical outcomes, so no one can level the accusation that its posturing or style over substance.
Whether or not those accusations leveled at DCEU films were unwarranted remains contentious.
With that being said, I have a hard time believing Endgame will necessarily *remain* bleak. High stakes and sacrifice, yes...but unforgiving? I do expect some kind of uplifting payoff. Maybe I'm wrong. Could be that the payoff is actually Phase 4 (or whatever phase they're heading into).