What if that line about getting vengeance for his mother's death was Trevor speaking to Zobek/Death after discovering Gabriel wasn't responsible for Marie's death?
See, that would make too much sense, and it's been made very obvious that MS wants to pit the Belmonts up against Dracula. If Trevor found out that Gabriel was not responsible for Marie's death due to being controlled and had since then not only taken revenge for the act but also saved the world TWICE and gave up his humanity specifically to do so, he'd have to be pretty emotionally stunted to take that information and continue with "I still hate you vampire dad!".
Plus since the Belmont hunt Drac!Gabriel to modern day times, how much do you want to bet that either that huge gaping plot thread is still dangling right in front of everyone's face
OR Cox forces some other "unspeakable act" upon Clan Belmont for them to blame Gabe for in order to keep things moving along? It's the only explanation I have for everyone conveniently forgetting/not knowing Gabriel saved all of humanity twice over and got super screwed over in the end. (I'm sorry MS, but you made Gabriel
The Woobie and I can't see him as being anything but the tragic hero/villain now and I want my catharsis for him, dammit!)