Why in particular? Most of the series is just dumb fun. I'm not saying it's all dumb fun, don't generalize me with that crowd, but it is generally not a story that tries to be complex, and a lot of the character development is rather generic and predictable with the exception of Piccolo.
Saying the Buu Saga is top quality even by the standards of "most series" I find very disagreeable. Controversial topic but, imo, Buu Saga is probably the weakest Z arc by far, for many reasons. I think the Cell Saga was one of the best though.
I mean it's probably an opinion thing. If you care mostly about action and fun adventures and everything in that category, then sure I can understand that. I'm more of a story guy and I focus on more subtle, complex stories with a lot of depth and detail to both the plot and characters. A story like Arcane.
But as far as shonen anime goes, HXH, to me, is like a better version of what Dragon Ball wanted to be as a franchise.
Also, while I agree with you on how the 23rd Budokai to Frieza Saga is the peak of the series, the Red Ribbon Army Arc was mid af, Tao was the best part by a mile but he got ruined later in the series.