I believe he means, once you've leveled all of your epic trees (10, currently), and lets say you did that on your first run through of 21-25, that the next time you do 21-25, you aren't unlocking anything for the NEXT time that you decide to do the TR grind (new class released, perhaps). I see the validity in it. When you TR, assuming you don't just do the same class more than 3 times, you get a nice free past life passive for your grind. Once you have grinded all of the epic destiny xp, you gain nothing more (permanent) from the 21-25 grind, assuming you TR again in the future.
I jumped the gun on taking it as he didn't appreciate the epic destiny xp that we get to keep, but that isn't his point, I don't believe.
I think we all are appreciative of the epic destiny xp that we get to keep. People just appear to be concerned about the future and how this pans out, as more and more classes are released, and people want to keep their completionist feat, I suppose.
I personally don't mind the 21-25 grind again, because I like to grind. But I can see the point of 'the other side' in this thread.