What's wrong with saying "Kamen Ride!"?
Just for the fact the term "Kamen" in its presentation has no meaning. IIRC, in KRDK, "Kamen" was never explained to have meaning at all. Not even saying it was a "Ventaran" word for "mask" or something of the like.
Honestly, the show could've been renamed "Ventara Rider" or "Mirror Rider" and still hold the same meaning to the target audience.
I believe something along the lines of "Advent!" would've been nice for KRDK. Simple and neat.
Plus, I can't unsee Richie's 'derp henshin' face when I hear the term as a replacement for "Henshin."
Maybe if "Kamen" was given a definition, even fictional, maybe would give the term more power than just being the titular characters trying to be burned into children's minds.
I can see "Kamen Ride" used for Decade's henshins, as his power derives from the others. I just believe the others need a unique phrase to their own universe.