The XS has a bass boost over the M80, so it is a more bassy headphone than others' on-ears. Still, its treble extension is much better than the similarly-shaped M80, and its form factor is truly amazing.
I tend to EQ down the bass when I use the XS, but it is my go-to headphone while walking about. The sound isolation is just enough to give good awareness of what is around without interfering with listening.
As for bass distortion, Tyll has the plots here, 3/4ths of the way down on the left.
The XS has less bass distortion than the M80. Even so, high volumes on an on-ear headphone is a recipe for disaster. It's simple physics: smaller cone -> less surface area to push -> higher excursion -> more bass distortion.