I do think it's true that Wanda and Pietro no longer being the children of Magneto is not a huge deal to either Wanda or Magneto, but does really impact the much more limited characterization of Pietro.
Wanda's got that whole Chthon thing going on, as well, so Mags isn't always as front-and-center in her personal drama.
So, if anyone is gonna get the 'together, you and I shall rule the galaxy' speech and his hand chopped off for saying no, it's gonna be Pietro.
Edit to add; I love the misspelling Magento almost as much as Rouge. I want Ian McKellen to play this fabulous Magento, who is almost exactly like Magneto, except he's *way* too into his purple cape...