Incorrect is thus subjective. There is no clutch slip in a sensible stage 1 with TQ output called at 340. As for saying it has nothing to do with MDNORM, it absolutely does. The ECU will never report more than what MDNORM is capped to.
There is nothing subjective.
If you reduce MDNORM from 500 to 340 on any DSG box, the feed-forward will be insufficent and the clutches will be CONSTANTLY in the microslip adjustment.
They will be slipping much more than the microslip target non-stop all the time on any increasing torque gradient. Adaptation will also do jack shit, because while on increasing gradient the control will be constantly undershooting, on decreasing gradient it will be as well, as they will be grabbing too hard and the adaptation cancels itself out.
To even suggest such a thing is "okay" means having ZERO knowledge of how the DSG regulates clutch pressure.
If you want to cheat torque a little on the top-end (and you will still have slip issues, but at least not in all daily driving), there are much different methods. You should never
ever change mdnorm on any DSG box to underscale reported torque, if you care at all for the longevity of the transmission.
Just because you don't see it slipping 1000 rpm, doesn't mean it's not there.
I really suggest educating yourself a little more on how the microslip controller and the feed-forward works before making stupid statements that someone is going to take for gospel and damage their gearbox.