Throughout history, every device that has incorporated a trigger mechanism has had concave triggers... until the Sixaxis.
The problems caused by the ridiculous convex trigger design were so widespread that 3rd parties began to sell concave triggers that clip over the original ones. Unfortunately, they come off far too easily and cost way too much for a tiny lump of plastic.
Sony had the opportunity to remedy the problem with the release of the Dualshock 3, but instead decided that they were right and LITERALLY EVERYBODY ELSE IN HISTORY was wrong.
Controller too small? That's a matter of personal preference.
Asymmetrical analog sticks? That's a matter of personal preference.*
Concave triggers? That's a matter of COMMON SENSE.
$100 to any person that can give me 1 good reason for having convex triggers.
If you get pains from the position of the left analog stick, why don't you get pains from the position of the right analog stick? The sticks are symmetrical and, presumably, so are your hands. Unless one of your hands is a wanking claw, your argument seems to defy logic.