Depends how much you value a postseason appearance. This trade single handedly blew a postseason spot. Had it not been done I think most everyone can accept that the Brewers likely were in the postseason. Maybe not as the division winner, but certainly as a wild card. Possible they still missed it, sure, we can't exactly go back and find out....but logically, they would have made it with Hader on the team. Stearns understands that they really blew it making this trade and falsely believing the team would still be fine. It just was not a good trade.
Could we get a bit lucky and Gasser turn into Brandon Woodruff, maybe...but it is going to take a lot for it to offset what a postseason appearance would have meant and whatever Hader would have garnered in the offseason or next deadline. Because let's not forget, keeping Hader didn't mean we would never get anything. We probably would have gotten a similar deal in the offseason or next July. As good? Maybe not on paper...but I doubt it would have been a bunch of random lottery tickets.
I am not sure Gasser becoming a 3/4 starter is really going to make it worth it. Missing the postseason after making this trade is a big black eye and a huge value lost. Gasser is a decent prospect, but hardly something difficult to find. We could have taken all the revenue from a wild card postseason appearance and bought a couple team's competitive balance picks. That would have been better than Gasser, in my opinion.