Not entirely true, though the fundamental argument that the Deluge isn’t great as a live looper, still remains.
However - synced recording is very much possible. By setting one of the track’s oscillators to External Input, and then having the Deluge sync whatever source you got coming from the outside to its clock, you can start and stop anyting controlled by CV or Midi on a perfect note. Getting loops with perfect start and end points is quite possible and easy, with the Deluge.
Also, sampling doesn’t need to record anything internal from the Deluge, you can set it to record only external stuff and then switch the internal audio souces back on again, when you’re done.
As a sampler, it’s pretty great for all kinds of purposes. As a looper, not so much.