Yes, the coolness list. I should add it as a separate point. Don't you feel strange that it's never explained why Rin doesn't put him on the list?
He never explains it out loud, but judging from who is on his list and comparing them to Renzou, we can figure it out ourselves...
I think what Rin thought was uncool about Renzou, from all that Rin knew about Renzou, is that he was always avoiding work, that when he was forced to work, he wasn't working hard, and that in addition to not working hard, he was constantly complaining.
Rin also repeated that Renzou was uncool, right after Renzou said it was more troublesome not to talk to him than to talk to him. Which meant his main goal was to avoid troublesome things. Which is the type of attitude I think Rin thinks is uncool.
Back to the misjudgment, it wasn't just about uncool. Rin said "I agree with you for the first time", like how Bon and Izumo described each other, which implied "I always disagree with you". We know how Bon and Izumo disagrees with each other, but there isn't any clue how Rin disagreed with Renzou.
I think that, for the first time for Rin, Renzou seemed serious about something and was ready to work hard together with him to achieve something they both wanted. That's why Rin was so enthusiastic about this. But when Rin said it was the first time they agree on anything, that was an overstatement.
At that time Renzou (seriously) expressed his concerns about Bon, and then Rin answered (or even interrupted) them.
You're right, I forgot.
Still, it's the same explanation, I think Rin thought Renzou was uncool back then, so he didn't care much about him, and so, didn't pay much attention to him.
Like previous one, here the point is the tendency that Rin only talks to Koneko when it's more natural to talk to both Koneko and Renzou.
Same explanation, I'd say.
Rin said he'll support Bon no matter what he decides to do. I don't think that's similar to his attitude to Renzou in chapter 45. And Koneko's question wasn't really about whether to let Renzou do what he wants. It was about why Renzou didn't choose what he is good at and likes to do.
You're right it's not the same. But I'd say it's similar.
If Renzou isn't taking the exam seriously or isn't working hard for it, it's his choice. All Rin or Koneko could do is tell him to "take this seriously" or to "work harder", but he already knows that.