@Kam14 Feel the exact same. Was pretty put off by their romance initially and tried to support it, but the reasons you've stated made it awkward for me.
And can't say I like Rei playing matchmaker either. Though I understand the author trying to dedicate Akari her own room for growth and introspection, this just feels forced and awkward, as well. Admittedly, some of my discomfort comes from how Shimada and Sensei look like they're in their late 30s, early 40s to me (Though I believe they're both actually in their mid 30s?).
I believe they're actually supposed to be 31, both of them. Someone said so in a previous chapter comment thread, at least.
I do admit it's a bit odd... to be honest, she should have matured through the progression of the story up to this point, especially after the bullying arc
which is literally the origin point for him realizing how he feels about her in the first place. Seriously, he goes on about how she saved him by not giving up on what she knows is right. I very much get that. I champion that moment, his promise to stay with her, as the point where he started to seriously fall for her, not to mention it was the impetus for the largest amount of character growth he, himself, goes through.
But after that arc, I do agree that she feels like she went back to square one, for the most part. I understand the value of her finding her happiness again after all that pain, but they can have her grow, too, right? Maybe I'm not seeing it as much.
Or maybe it's because we're looking at the wrong moments. In fact, whenever there's talk about grandpa's shop or whatever, it feels like Hina is the one seriously thinking about the future in that respect- her maturity comes to the surface then. She's just also extremely energetic (one of the things that Rei loves about her) and this results in many child-like moments.
But still, I fully understand why he falls for her in that moment. Akari wouldn't have done anything like that. Only Hina could have clung fiercely like that, burned as passionately. And it's that fire in her heart that melted his frozen heart far more than Akari's sheltering older sister presence. Akari couldn't stand firm in front of the bullying like Hina did- she crumpled, and felt like she failed Hina, during that arc. And Rei was there to support Hina as she fought for her ideals.