I was trying to make a rub similar to Tx BBQ Rub on my last cook and used lots and lots of brown sugar. I smoked four butts low and slow with no foil until they came of the wsm. The end result was a " for the most part " burnt bark.
The bark looked right but it was hard as a rock over half of the surface area. It was like jerky on the outside. The sugar was burnt. No question about it and it burnt below 250 deg.
Good bark should be firm on the outside but bite thru tender at the same time.
Like a warm M&M.