Cosmetic mechanic
It’s a blur, not a stealth, when dodging that the large characters get so they don’t have weird animation clipping through terrain etc.
The Asura do flips. They front flip, side flip, and back flip. This is completely unique to the race, and is awesome. Gives it a nice class feel when combined with Thief, and is only possible due to their size, where an upside-down flipping Norn would be ridiculous.
One of the cool things about thiefs is their feature to “blur” when they dodge. If i wanted a character that did flips/rols/etc i would have chosen another class. That “blur” as you call it, makes the thief unique by itself.