I sure hope Roddenberry later backtracked on the idea that the original series was a dramatization of the events, that was definitely one of his more pretentious and overly-dismissive moments. Though OTOH he could have had affection for the show even regarding it as not exactly canon, as that it shouldn't very much influence later works.
Anyway, I think he'd rank
TNG Seasons 1-4 as equivalent and at the top, followed by original series 1 & 2,
TMP, original series season 3, animated series, then II-IV, VI and V. More or less based on how much he was directly involved with it aside from liking
TNG seasons 3 and 4 and coming to regret and be dismissive of the animated show.
Yes. There would be the gravitas of Savik's character and the weight of her prior history of ST II & III brought to bear and cashed in on. All that trust and affection she had built up.
I don't think it would have made sense to bring back Saavik and try to conclude her character, and with Alley playing her (pretty much as in II), as a sequel to both II and III when she already seemed a suddenly very different character in III then she did in II. But OTOH ...
Especially factoring in Saavik's melding with Spock to get him through ponn far in III and then flipping the script and having Spock rip the necessary information out of her in VI ... WOW! That sequence would have been second only to Spock's death scene in TWoK. Would have taken things up at least 2 full notches!
There would have been too much affection for her betrayal to seem believable or a satisfying conclusion, at the least it would have needed more screentime and attention which the film and filmmakers probably didn't have time for. Plus a new young character at the helm better conveys the theme that it's the passing of a generation then bringing back a character first seen in II/1982.