I agree to a certain degree that we can’t expect every player to complete everything, however:
If a person complains about “not enough content” without any specification what kind of content they want more of, like the topic starter did, then we are perfectly allowed to point out to content that this person probably has not completed yet, which would be a solution since it would give him stuff to do since he did not specify what he actually wanted to do at endgame.
On the other hand, if a complaint is more specific, like saying “there aren’t enough instances for endgame players” then that’s a thing we can talk about, because then they actually pointed out what kind of content they want more of and we can have a discussion whether more instances would be ok. However, that’s not what the topic starter did. He just said “QQ lack of content, moar lvls plz”, in which case we can ask him “Since you did not specify which content you like in particular but just asked for more stuff to do, regardless what it is: Did you really do ALL the things you can do at high level?”.