I'm sure we've all heard statements like those somewhere. People are angry because this harmless slice-of-life show involving cute high school girls is now the new hottest thing instead of their manly anime.
I would take issue with two parts of this statement (which I know is hyperbolic and not entirely sincere, but I'm responding anyway)
i) I'll fully admit to being annoyed at the success of such shows, but I don't think it's about "manliness". Dai Sato once put it as the difference between "atmosphere-type" shows and "difficult-type" shows, where atmosphere emphasises character and difficult emphasises plot. I think that's too simplistic and naive a distinction, but certainly I'm more interested in shows with Stories with a capital S (yes, K-On has a story, but... you know what I mean!). I would consider, for instance, Orange to be a "difficult-type" show, despite being a character drama, whereas Amanchu is clearly an "atmosphere-type" show.
ii) It's also difficult to get my head round K-On being the progenitor of this phenomenon. Note the top 10 anime of 2002, for instance, as voted for on 2Ch - while King Gainer and Haibane Renmei are at the top, and there's a pleasant appearance by Twelve Kingdoms in the list, the rest of the list is things like Sister Princess, Tiny Snow Fairy Sugar, Azumanga, Figure 17 (which, although quite plot heavy, heavily played on the moe relationship between its two 10 year old female leads) etc. It even has Galaxy Angel in the list, which is one of the most vapid cute girl shows I can think of...
The point being that this is probably something that people have "complained about" for a long, long time, if they are in a particular segment of anime fandom.
I would actually say, however, that we seem to be in a good spot at the moment. Not that I'm watching much anime really these days, but looking casually at what generates discussion and seems to be airing, there seems to be more variety and choice - not necessarily quality, mind you - then there was in the early 2010s, and I think that's reflected a little in the topics of conversation on AnimeGAF (having lived through K-On's explosive popularity and the probably-quite-brief-but-felt-like-an-eternity Precure obsession phase). We've had shows taking chances visually where you wouldn't necessarily expect them; noitaminA is in a diverse phase of programming this year; there are shows that appeal to all sorts of audiences.
I'm sure that'll all change once the next waifu wars show kicks off or whatever (or something Rem-related happens in Re:Zero...) but currently there doesn't seem to be that much worth ranting about.
