Personally, I read it that way because I enjoy it being Spock's different approach to legacy. McCoy has Joanna, Kirk has David and Spock has someone who he (in the Pandora Principle) defends and gives the care they deserve whilst helping deal with their mixed heritage. It is both what he didn't get and is a nice culmination of all of Spock's growth from TOS to the TMP era in the same way David represents Kirk's pattern of abandonment. Likewise in TWOK she's presented along with David as part of the next generation as our main cast are now no longer in their prime. David is explicitly Kirk's son but I don't think it's too much of a leap to see Saavik in TWOK as occupying the role of Spock's (figurative, not literal) daughter type figure. So that's why I prefer to read it as like a father-daughter relationship.
Okay, maybe. But that doesn't make Saavik his literal adopted daughter, which is what ThetaSigma (any relation?) claimed they were.
I would also add that it does become creepier given Spock found Saavik as a child and there's a vast age gap.
It's not vast at all. In Vulcan's Heart, Spock and Saavik marry in 2339, more than 50 years after The Wrath of Khan. If we go by The Pandora Principle's birthdate for Saavik, she'd be 75 years old at the time and Spock would be 109. So they differ in age by only 30 percent, and it's akin to, say, a 54-year-old man marrying a 37-year-old woman -- not too far off from Leonard Nimoy's second marriage, in which he was 58 and his wife was 46.
And yes, he found her as a child, but that was 65 years earlier!! Surely that's become just a small part of their history by that point, long since eclipsed by their decades of interaction as adults. It's condescending and sexist to treat Saavik as if she's still a child at that age. She's a grown woman and perfectly capable of marrying whoever she damn well pleases. So what if she was a child decades before? Everybody was! Who she is at the time of the marriage is all that matters.