Biased much? You are literally defining stupidity on the basis of who you like.
Me? No... I like all the main girl (Bella and Maya less, I must admit, but it's not a dislike, just less) and most side girls. And Jill's not even my main route. I play "The Others" 1st, then Sage's, and, only then, Jill (and probably would play a solo Josy first if it ever existed). I just don't think she's stupid in the literal sense of "lack of intelligence, understanding, reason, or wit, an inability to learn." In fact, I think only Arieth qualifies as this, and none of the girls are really stupid in that sense. I was just "lawyering" to prove that you pick isolated events, acts, or speeches, every girl can be qualified as stupid. But even you said that:
Well in truth our whole approach is flawed as we are trying to establish general intelligence based on isolated anecdotes. Any specific situation may be unusual for the character. You need way more examples to draw reliable conclusions.
So I rest my case. But, if by "stupid" you meant not "street smart", I agree, but I think "naive" is a better word to describe that. She's introspective, socially awkward, and inexperienced. About the Tybalt thing, I just think she has a good heart and, more importantly, she's living in his house, so it's good to have a good relationship with him. However, she never acted as a friend in the sense she goes out with him or do things together: he even had to blackmail her to do simple things like playing tennis or going out to dinner, which are things friends normally do together. She was always rejecting and deflecting his advances. The most she used to do was have some lunch with him in the house. She was polite. It's only when he crosses the line, blackmailing her and stealing her points, she ceases to be (helped by the fact most of his frat brothers are also pissed off with him).
Well then let me counter:
-Sage: People who kept telling her Chad was gay but she wouldn't listen = zero. How is Sage stupid for not realising something no-one else realised either?
-Maya: A teenager who trusted that her father wouldn't betray her. She was unlucky in having an untrustworthy father, but if trusting your parents is stupidity, very few people can be called smart.
-Bella: There have yet to be ANY legal consequences for her relationship with MC. You are arguing that there should be, but even the real world doesn't work like that. People get away with things all the time. And since she is well aware of the risks her behaviour is simply reckless. She is taking a risk. It may lead to tragedy, but it may also lead to happiness. This is not stupidity.
-Josy: Well she is definitely insecure, but not stupid as such. Getting into a hobby so that her profile won't look basic is definitely something I wouldn't do. But if she actually likes what she finds and doesn't simply do it for the sake social media, how is it stupid?
Compared to this:
-Jill: People who understood what Tybalt was like within minutes = everyone else. Granted only Bella kept telling her so, but literally no-one else takes Tybalt at his word. This is stupidity. True she is not Arieth level stupid, but still more than any of the others.
Main Girl Smartness Ranks:
Bella>Sage>Maya>Josy>Jill
About the other girls, I admit that with Sage I pushed too hard. She even suspected Chad was cheating... She only didn't know it was with a dude. As I said, I don't think any of them is stupid in the sense of lacking intelligent, but some do "stupid" (or foolish, reckless, inconsequential) things, which is different. Though she's probably the smarter (no wonder, she's almost two times the age of the other girls) and, maybe, the most intelligent, I think Bella tops 'em all in stupid things of risking lose her job (and career) dating a student, but she has the excuse of being in a smut visual novel where every faculty member is as "stupid" as her in that sense -- no one can resist our hero's charms, right? Maya's foolish act could be excused as you said if her father weren't who he is... But, indeed, it's an ambiguous case... My issue with her is that everybody talks about Josy, like, she's bland and so on. I don't think Josy's stupid in the sense I'm using here, but I agree that I wouldn't probably have a very interesting with her. However, what about Maya? What intelligent thing she ever said? It's only because she care about wOmAn AnD sOcIaL iSsUeS and is a damsel in distress she's intelligent? For me, she's the worst of the five: less intelligent and also closer in naivety to Jill.
B.T.W., for me, this is just a debate about a theoretical disagreement... I'm not in pissed off in any way (and I don't think you think I am, but, you know... Internet... Typed words can be misinterpreted... Better be cautious). You can badmouth Jill as much as you want; and I'll keep thinking she's not stupid. It's cool to see people's different takes and opinions. At least we have some discussion different from "alady here; alady there."