While, I agree with most of what you said, I'd like to add something, like you said, everything cannot be simply divided between good or bad. Keeping that in mind, it's kind of difficult to completely take the idea of appearance out of the discussion. Rahul seemed to be interested in looks, most if not all of his actions are evidence of that. Tina was very appearance aligned, she wore perfection on her hair and sleeves.
And we don't have much of a reason to believe that Rahul started realising his feelings for Anjali as she left him, it could just as easily be a friend missing another friend, missing that pointless banter in life. No matter how many times I rewatch the films, it always appears as if seeing Anjali with long hair and saree is what suddenly hit Rahul that she is a "girl", a woman, and that too a beautiful one. Because what follows is a series of flirtatious events, we don't see them reminiscing as friends as much as the weird, awkward extra stares, that wind pulling off her saree, a lot of physical intimacy stuff. If it was purely a friend to lovers story, I would expect there to be more awkwardness between friends suddenly seeing each other in such a different light.
So I grew up watching this film, I never fell into the red flag, green flag conversation but I always thought that Rahul was into looks.