Dai
Death Scythe
I see this all over the anime fan community, but the term slice-of-life gets misattributed to a lot of shows. Pretty much any contemporary high school story tends to be referred to as SoL, regardless of what it really is. It's interesting that the things you didn't like about K-on are practically the defining elements of the slice-of-life genre. It sounds like you you didn't want it to be SoL; you wanted a coming-of-age drama. Conversely, Sound! Euphonium isn't SoL at all; it's pure coming-of-age drama.I didn't get the K-on hype either after watching it. The characters were fun enough, but reading my mini review from a few years back, my problem seems to be that it had the hook of girls in a band, but then they did anything but play their instruments for episodes on end. I also said there was no plot or character growth which does seem a little odd for CGDCT, but when compared to say Yuru Camp it pails in comparison. I think it comes down to the original work with Yuru Camp being a manga and K-on being a 4-koma so, without having read it, I guess there's not much linking the skits and writers on the show didn't fill in the gaps too well either.
Sound! Euphonium is still my favourite KyoAni which is SOL, but not in a CGDCT type of way and that was a novel adaptation.
I hated K-on for years precisely because I was used to high school band stories being inextricably linked with the coming-of-age archetype, and was frustrated that they wouldn't take the music seriously. It's only in the last year, after acquiring a taste for SoL shows, that I reassessed K-on and started enjoying it on its own terms.