>>6421415Although they're generally similar, there are some differences which can get highlighted in a show like this.
Kuuga's variants have the special abilities associated with each one (like super sight), Kiva's variants have the monster-type fighting styles even without weapons (Decade used that only once though, Kiva Garuru vs Exceed Gills).
Agito's variants are basically worthless though, just the generic variations that everyone else has. Den-O's about the same, although Decade added sumo fighting to Axe form, making it different from the other weapon variants, and basically used the other ones for jokes.
Now, for Gokaiger, they're giving much more focus to each team's theme, more than the original series in some cases, basically only using each team's special abilities and weapons, giving each one often much more unique fighting styles than they originally had.