Exposing Dano or Perreault had absolutely no bearing on the expansion draft. In fact, Dano was left unprotected. The trade down with Vegas was to protect Enstrom, who had waived his NMC. At that point, Enstrom was a key top-4 D for the Jets as they were going into the 2017/18 season, in which they saw themselves as a strong contender. Losing a top-4 D is not something that a top team will want to do. If the Jets had to protect Enstrom, they would have lost one of the following:
Myers, Little, Copp, Lowry.
So the choice was losing one of: Enstrom, Little, Copp, Lowry.
Instead, they lost Thorburn, and in return moved from #13 to #23 pick.
I don't think this was a bad decision considering where the roster was at the time.