5 years, we've finally reached the end boys.
It was a fun, fluffy romp. Good stuff.
Thanks to the translation team.
In particular, and this is apparently an unpopular opinion, the character of Rin has been useless throughout the whole story
You're both correct and incorrect. While the set-up was MC beating the FMC and then confessing to her, that was not really the point of the story. It was just a staging to spur interactions between characters, the actual confession was actually fairly unimportant (though it felt important due to how long it was dangled in front of us).
So Rin was unimportant to the actual confession story, nor did she ever make our boy waver, but she was another fun character who the others interacted with - in this case she perfectly fulfilled her role.
To put it simply; the story (the confession) was unimportant, the character interactions (and thus Rin's as well) were, as they were the entire bulk of this comic.
It's like being upset that K-On didn't end with the band becoming the next Beatles, when music and the band's career itself wasn't actually the point of the series.