Like emiko stated, it really depends on whether you like the songs/artists or not. If you like something then you will less likely say that it is overrated.
I did notice though that I like songs of A LOT of different k-pop artists, while I can't say the same thing about j-pop. Most of the time there's atleast one song that I like from a new release of a kpop artist. One of the reasons could be that they're all 'the same', have 'the same' style. So if you don't like that style, kpop could be overrated for you. But yeah it could also have other reasons
And I've noticed that there was a period that everyone had discovered jpop and was all into it. Now, jpop has faded, I notice more people are getting into kpop, they try to discover other things. So that could be a reason why it's all about kpop lately. Or it could be vice versa... it's all about kpop so that's why people get into it easily, I guess it's a neverending circle XD
And about the comeback thing... yeah I never understood it XD But I like kpop since I've got the feeling that the artists are active in all kind of fields XD