It really makes no difference to the Brewers if he gets hurt or not. I'm not disagreeing with you though. The Brewers chances of winning it all, even with Burnes, were slim at best, and their chances of being able to afford him in Free Agency were nil.
Under those circumstances, trading Burnes made far too much sense for it to not happen. If you subscribe to that perspective (as, I think, we both do), the only question is the return, Last night, I hated it. I really wanted Mayo in the deal. This morning, I'd changed my mind. I still wanted Mayo, but a high-ceiling LH (hopefully) starting pitcher, a gold-glove calibre SS who slashed .321/.378/.507 at AAA last season and, effectively, getting the comp pick they would have gotten for Burnes a year early isn't a bad return for one year of Burnes.
It helped me to remember that with Hoskins being signed, and Black likely making the team this year, the need for Mayo wasn't as great as it had been. Plus trading Adames along with a surplus OF could help bolster the pitching a little... 🙂