Going from 1.072 to 1.012 is 83% ADF which is above the range Wyeast suggests for 1056
of 73-77%. i.e., It did ferment lower than one would expect for that yeast.
Your temperature range sounds fine. Was it in that range for the first two days also?
Did you use a $hit load of pure O2 by chance--like 3-5 minutes? A serious hot alcohol taste like spirits is usually from a hot fermentation or a serious OD on O2.
Only being 12 days wild yeast or bacteria couldn't have so quickly fermented the long chain dextrins.
The brown sugar is only 3% of your total grain bill so I don't think that is the problem. If it were a lot higher that could be a contributor.
What was your mash temp? Did you mash in the 140s? I wonder if you made a really fermentable wort?
That is my thought process. Maybe that will jog some ideas in what you might have done that you didn't think to mention. Hot alcohol doesn't usually mellow out much but give it time. You never know. Good luck!