You have to think of the trade in terms of time frames. It's no longer learning time in NJ unless you're providing immediate value a la Luke, Nemec and Casey.
Holtz needs time and it's unclear what he really is. The Devils had a similar sort of player in Zacha with respect to how back and forth his progress was. He got all the time in the world to develop because of the general state of the team, but today would have gotten the axe much faster.
It's pretty clear that Cotter brings some speed, some hitting and has hands good enough to get you a zone exit with consistency. That's all you need for a team that was running AHLers with regularity in the same slot last season.