I think there's a big difference between the problems of those two.
Decade has many unexplained elements, although most of them are tied to specific stuff of the individual worlds, there are some connected to the main plot, like Narutaki. However, it followed on the early foreshadowing, never contradicting it.
Kabuto, however, did contradict some foreshadowing. Yuri's drawings and Tendo's early comments about getting the belt from the sun turned out to be utterly irrelevant. In addition to that it also had some unexplained events, mainly how some secondary Riders ended up with their Zecters, although they're generally less vague than the unexplained mysteries left by Decade.
Still, I think Faiz has more plotholes than both. Just the Delta belt by itself takes the crown.