For something of a series finale, It would have been too much. Saavik as a character was a breath of fresh air when she appeared in TWOK and it didn't feel shoe horned in at all. She was capable and smart when matched with the original crew while still leaving some areas that we could have been further developed.
And on a more personal note, Star Trek didn't need to screw over another female character. I know Valeris falls under that as well. But unlike Valeris, I still want to see more of Saavik. If STVI ended with Saavik being the traitor, that would have been the end of it.