Hwang in the original Soul Edge was 90% mitsurugi.
X didn't steal his moveset... She had an original kit.
Yun Seong is also his own character.
It's more complicated than that. Hwang was the alternative to Mitsu for countries that were anti-samurai with some move variations, but it's Mitsu who has the moveset overhaul when he next appears in Soul Calibur.
Hwang has some of that old stuff mixed in with X's moveset in SC and then SC2 Assassin is a remix of that stuff plus some Yun Seung moves, which gets remixed again in the Hwang style Chinese sword custom in SC3.
At this point he's as much a clone as Nightmare - Seig, Mina - Kilik, Sophie - Cassandra, or Raph - Amy. You could make an argument for any of them at one point in time, in either direction in some cases! Ultimately it's just semantic bullshit over who is legit and who's a copy.
Bottom line, at this point it's readily apparent that all SC6 characters have highly unique movesets even if they share similar weapon styles, so arguing against the inclusion of a clone seems silly.