I'm gonna have to rewatch 11 and 12 again to really pin down if I read too much into it or if you didn't read enough, but I didn't watch 11.5 while the show was airing and it was very easy to connect the dots and tell that Oreki's attitude at the beginning of the festival arc wasn't really the same as in the previous arc. He gradually gets more involved and starts being more himself again, but that's normal, it's not like what happened in 11 ruined his life lol.
11.5 itself is pretty meh as an overall episode, and the parts that address Oreki's character arc are just making explicit what can already be inferred by the two surrounding episodes.
11.5 itself is pretty meh as an overall episode, and the parts that address Oreki's character arc are just making explicit what can already be inferred by the two surrounding episodes.