It doesn't matter. I doubt anybody would be dumb enough not to notice that after a while, the load provided by a pair of dumbbells would be insufficient for continued gains, both in hypertrophy and strength. And the "issue" on whether to use dumbbells or barbells, isn't even an issue. If someone can constantly progress using a dumbbell, then go ahead. But once the plateau has been hit, you either mess around with T.U.T or platform height, or R.O.M or the most convenient way? Use more weight