There are characters who use more haki than Luffy in his gear 4th, but they never run out of haki. It's only Luffy who has this stupid drawback which doesn't make any sense whatsoever. Luffy now has awakend his DF ability, and it seems that–as other awakenings–gear 5th doesn't have any drawbacks. But what about gear 4th? Like seriously, this is trolling at this point. Plus gear 4th is useless, it's much weaker than ACoC Luffy in his base let alone gear 2 combined with ACoC.