My hand could never reach the run button in the arcade. It always felt slapped on to me. It was too instant as well. Forcing a double tap motion makes run-canceling harder and less abuse-able. It's a good thing.
I'll admit, on an arcade stick the run button can be somewhat awkward to reach with your thumb. On a pad however, there's no competition. Map L1 or left bumper as your Run button and there you go. It's right above the directional pad. It's so simple, convenient and well-executed it blows my mind that no fighter has replicated this model.
