Yea this is true. A few characters have not been explored. But a majority have been.
A great explanation for you would be Ayane vs Ein. The characters share a similar playstyle. Bait and Whiff punish (or more specifically, whiff punish). Unfortunately, Ein fails in comparison.
Ayane controls space better than Ein ever could while still sharing some similar tools as well. She also runs better cqc than him, with quick mixups and great keep out/getting herself out tools to get herself back into her comfort zone.
But no, Ein is fine, right? I just need to play better right? Or switch my character even though I like him better as a character. Maybe I don't [want] to play as a girl (Hitomi) to get the same results or better yet, a ninja (Ayane) and work twice as hard simply because these players are scared of having to deal with another threat.
So that's my explanation in example. This applies to Hitomi as well. Hayate in a way but Hayate is a different ball game completely since he plays a primarily aggressive spacing game rather than defensive one.
i feel the same since i play with majority of the male characters outside of hayabusa and hayate..the males may have more strength but if you get out poked by a faster character strength doesn't count