I found the R2/L2 triggers too unresponsive in a quick race. If you really need to brake hard, it just takes too long getting the trigger all the way to the maximum position (they are quite springy, you know). And for slight braking you can still tap the R1/L1 ever so briefly, I'd imagine it does roughly the same as pressing in R2/L2 ever so slightly.

I guess lots and lots of playtime will tell (so bring it on, SL!)