I've gotta disagree. I've replayed Step One more than a fair share of times, and Opal really can vary a lot depending on the MC's personality. She's got like almost twenty-five alterations alone between how she interacts with the MC and the text about her, or her and MC's relationship. And that's just me bare-minimum counting.
For starters, she's stricter with and more cautious of rowdier MCs. With quiet/shy ones, she caters to them (not too much, because overall as a character she seems to desire that MC to be somewhat independent) and is pretty chill with confident but more mild-mannered MCs.
One of my favorite interactions is that during the prologue, if you have a lactose intolerant MC who is rowdy, when Yusuf promises he won't give them dairy products if they ever happen to come over there without her, she tells them, 'Thank you. As you can see, I need the help.' Something she doesn't bother saying with a less 'wild-child' MC type.
Also, in the new Halloween moment, if you play a brattier MC who also doesn't care for following the rules, she will make sure she slips you more pieces of candy than Qiu or Tamarack. With a more well-behaved MC, she knows they won't make a fuss over it and give them all equal pieces.
So, yeah, I can get not necessarily liking Opal's personality (she's not the coddling or doting type like the OL1 moms, which can be kind of off-putting for some people, as mothers are often portrayed that way in many games or on the entire opposite spectrum) as much, but you can't call her bland or say MC's choices don't shape the dynamic with her. Considering we're not even done with Step One yet, they definitely have by an impressive amount for it not to be a game that revolves around the MC and her.