I'll chime in and say that I do think that haki has made a somewhat negative impact on combat, but that I don't think it has severely ruined most fights. As others have pointed out, Law and his Ope Ope fruit threw a monkey wrench into things, and made "levels of haki" into such a thing. In that way, Law's power reminded me of when Robin was first introduced. Initially, it seemed she could beat any non-Logia like that (snaps), but then it became clear pretty fast that superior strength and speed was sufficient.
So for me, the big instances of my haki beats your haki bull, that's bothered me has just been - Law vs Vergo and maybe Zoro vs Pica, aside from that, I'm more annoyed with the schtick where seemingly OP fruit hax become useless later on just because of an opponent's haki. Law, Doflamingo, Hancock, probably Bonney if I had to guess. That said, someone posted an interesting theoretical explanation for this recently in this or the spoiler thread, that postulated that hax fruits could be focused in order to effect stronger opponents (their example was in Hancock's attacks at Marineford) and I found that to be a somewhat satisfactory explanation.
And as some have pointed out, haki has also made seemingly useless fruits - Biscuits and Mochi - powerful. Course, one could argue that Oda could have just declared that Katakuri's Mochi was hard as iron just because. Afterall, he did that with Mr. 3's wax, but at least wax is hard by nature.
And I'd also like to agree with whoever said it so far that none of Luffy's most recent boss fights have felt lacking in interest. Hody had his Fishman Karate and underwater combat, Caesar took his breath away, Doflamingo got defeated by Luffy turning into a beachball, and then Luffy had to contend with Katakuri being seemingly as unhittable as Crocodile was in their first fight. And luckily, many of the Strawhats still don't use haki, so I think there's still plenty of room for non-haki-centric combat.
Slightly off topic, one thing in this current fight that might have been way cooler if Law could have teleported Big Mom and Kaido is if he had switched say Zoro for Big Mom or something and tricked Kaido into beaning her in the head or vice versa with Big Mom accidentally attacking Kaido.