From that angle it could make some sense, especially since DiZ, Xemnas and Riku, the supposed main antagonists of this title, got wasted due to blackhole-Xion requiring all attention.
It is still ironic though that it comes to the "catharsis" factor since there are several other characters who "hurt other characters' feelings/are mean to them" (Riku to Sora in KH 1, Larxene to Sora in CoM, Marluxia to Naminé in CoM, Vanitas to Ventus in BBS etc.) and yet several of those actually have quite the fan following despite being "assholes" just as Saix is in their particular roles in these titles.