Present day Superman has been around for so many years that Morrison's "Superman at middle age" approach still works. Even with all the time shenanigans and rapid aging of his son, the current Superman has been around for about two decades or more if you take into account Death Metal's idea of everyone remembering their past lives.
But, if it didn't work for you, there's likely nothing I can say to change your mind. Given the situation they were in, I think PKJ, Morrison, and company did an admirable job of sorting it all out with a minimum of hiccups.