You could always assign the airbrakes to L1 and R1 if you don't like the analogue triggers, rather than using a crappy PS2 pad...

I think the issue with barrel rolls on the analogue stick is due to the positioning of the stick itself - it's at the wrong angle to your thumb (Sony should have swapped the positions of the d-pad and left stick years ago), and because it's totally loose and has a circular surround (unlike Nintendo's sticks, which have 8 notches) it's harder to gauge whether you are actually angling the stick exactly left or right.

Many failed BRs are due to the fact you've done something nearer to top-left, bottom-right, top-left without realising.