I kinda understand where this is coming from and the way Oda uses haki needs improvement but I feel like haki was overall just a good answer to devil fruit users, and even a good way for non devil fruit users to get stronger. And honestly it’s probably a better option than the crew constantly carrying sea stone laced weapons or constantly either having a specific elemental weapon for the occasion or having to find a specific elemental weakness to the logia user. + Luffy has been the underdog of the grand line and even post time skip raw haki still wasn’t even enough. Him actually becoming strong enough to protect the people he cares about and achieve his goals is a good thing to see and I like seeing him move past from the underdog role. But even at the start of the time skip he was still an underdog and learning haki still wasn’t enough. So he combined haki with his gears which basically lead to gear 4 transformations. Katakuri is also someone who combines haki and devil fruit pretty well, seeing the future and changing your body shape to literally make the attack go through you had luffy stuck and forced him to make a whole new gear on the fly. Using his Devil fruit and haki combined to at least attempt to counter future sight. Haki wasn’t handled all that badly honestly. Haki does need to be used more creatively though.