Remathilis
Legend
They were allowed and could choose to defile for more power.You wouldn't lose much if you took out arcane Bards from DS 4e, since I believe that the Athasian Minstrel was a theme. I don't have my books on hand, and I can't recall how some of these other arcane classes were handled.
Which worked because 4e had so many classes. 5e doesn't. So, removing a huge swath of them limits you to only a few options. Which is why Dark Sun would either need to loosen up on restrictions OR add a metric ton of new ones to replace what's lost.