To be fair, how many adventures has Reimu been on since her loss to Suika in IaMP? She certainly couldn't summon Gods back then, nor did she have Fantasy Heaven IIRC, so she has powered up quite a bit since then whereas Suika has only been in the other two fighting games (and the Aya spin-offs I think).
That's not even taking into account what happens later in this story. You could argue that Suika is not actually at her best with what happens next in mind.
In my opinion, due to her lazy and easy-going personality, her self in Wild Horned Hermit isn't much different from her self in IaMP, that includes her battle skills, unless her powers grow up as she ages which still wouldn't increase her power in a grand amount, since the gap time between IaMP and Wild Hermit isn't big. But that's just me blabbering.
