As an update: I’ve seen transcoded the original 1080 24pA DVCPRO-HD test clip to ProRes 422 HQ, then used Compressor to burn the DVD from that, and the results were dramatically better — no stair-stepping and only minor compression artifacts visible.
I also tried using Toast to make the DVD from the original DVCPRO-HD clip, and while the results were slightly better than Compressor’s (no noticeable stair-stepping), there were a lot of other artifacts.