I would have been okay with either choice... using Saavik as the traitor or creating a new character.
A much bigger problem for me is when they make a new character that's a rehash of Saavik. Spock's Vulcan protege, manning the helm, even using the same "quarter impulse in drydock" joke.
If they weren't gonna use Saavik, then at least make a new original character. Change something,
please. Make him a male, a science officer rather than helmsman, non-Vulcan.
As it is, Valeris is too much of a note-for-note knock-off of Saavik for my liking. That's bothers me more than the issue of Saavik's integrity.