I'm not really sure how I feel about the whole mother-in-law thing. It feels like a sexist trope, but I'll let someone else articulate whether or not it's actually problematic these days.
Think of it as a stealth retcon of the implicit sexism of "Journey to Babel," if it helps. Turns out that Vulcan marriages have a dominant partner based on the personal characteristics of the couple, rather than the gender or species.
That said, Vulcans really are a stupid culture. lol
I know it's a problem with all of Star Trek's cultures, except maybe the Bajorans, but one wonders how they have all these stupid rules while managing their reliance on logic.
I have seen the argument made that arbitrary and non-rational rules are necessary, typically from cultural conservatives. Given "Amok Time," I think we have to accept that Vulcans agree with this argument.
How they reached this conclusion.... well, I'm just going to deploy some handwavium.