Okay, I guess I should start out by saying that you completely misunderstood that thread between Haru and Rin? They're both drunk and both hit with the lost inhibitions event. They've had UST since they were twelve. This isn't a "that's it, the ship is over, all problems resolved" kind of deal. It's awkwardly kissing and two idiots not realizing what they're doing with each other. Rin is impulsive and this isn't "oh we suddenly love each other", but just a reflection on years of Rin having a crush on him. Rin is very physically demonstrative, even in a platonic sense, so with a lost inhibitions event at work, that he'd move to a kiss is a logical response, and not a "I've figured out all of my feelings ever that's it ship over" thing.
JL and I have played a looooooooot of ships together, a lot of which have included "UST that builds up until everything overloads". Haru and Rin can fall into that category, but Rin himself is impulsive, and aided by an event, he'll certainly be even more impulsive. This isn't some huge declaration of love, it's just Rin being a hormonal, stupid teenager. I can play the ship as I like, whether others feel it's "too fast" or better suited for museboxing or not... I mean. They're seventeen. "Feelings first, kisses later" doesn't actually work for every single OTP out there, and especially not for teenagers who've basically been obsessed with each other for years. They're stupid idiots. They're not going to deal with rping cliches. And, after seven years of playing OTPs with JL, we're bored of the dynamic and wanted to play an OTP that wouldn't fall into that dynamic.
A lot of what you're saying, honestly, is more headcanon than basic canon facts, and some of it is headcanon that I don't necessarily agree with in terms to how I've been playing Rin and how I think Rin is as a character. I understand you're coming from a place of wanting to help me out here, but a lot of this reads as "I don't approve of how you're playing this ship, this is how you should be playing it" rather than "this is ooc, and here's why"... and I can appreciate and respect your interpretations - but it's an interpretation, a headcanon, not necessarily "crit" based off something that I'm fundamentally getting wrong about his character.
Rin is physically demonstrative, Rin is impulsive, Rin is affectionate and attacks things head-on.
What I'm gathering from this, however, is perhaps I need to put more introspection into tags, which I do attempt to do from time to time, because it's clear to me that you've misunderstood what's happening in the thread. I do try to incorporate that into tags without going into heavy tl;dr every time, but I'll endeavor to do more of it with Rin in the future.
I am, however, relieved to know that you like how his intro was handled. I was a bit nervous if only because haha yeah, hard to know how someone from a sports anime/slice-of-life shenanigans would react to sudden new jamjar world with magic, and I definitely wanted to make him logically annoyed and WTF about things without making him too closed-off and jerkish, since that doesn't reflect his attitude at the end of season 1/beginning of season 2.