You can at least argue that Guentzel has something to gain from playing in the A, in terms of making that final pro hockey leap. It's a bad argument but it's there.
Pouliot gains nothing. This trashes what tiny little flare of confidence and hope he still had and goes a long way towards confirming another first round bust of their making.
Pouliot's only got about 70 games worth of work in the AHL in his career. That's really not a whole lot of development. Certainly not so much that he's got nothing to gain, nor was he some sort of dominant, "obviously doesn't belong" level hockey player in the A. Goligoski had 100 games and Dumoulin close to 200 and both were better players at that level than Pouliot has been.
If anything, the case can be made that he should have been cut in training camp, not that it's unfair to send him down now.
Far as Guentzel, I have no Earthly idea why he would be getting sent down instead of Wilson. Can't explain it.
If Wilson killed penalties or if he was scoring more often than he is that would be one thing, but that's not the case. And since Wilson's problem (insofar as just being a non-disruptive passenger qualifies as a problem) looks mostly strength-related to me, I don't see that there would be much improvement just waiting things out.
Only thing I can think is that the Penguins feel more comfortable scratching Wilson if they have to than they do Guentzel. But then, that begs the question of why the Hell Pouliot didn't go down last March and stay there.