Sure that Trolls can be an exception but nevertheless it really "disturb" me.
The balance of a rifle is not the same as for pistols... maybe with a customization of the rifle....
It can be fun for a "once upon a time big-apocalyptical-gun-justu-fight" or something like that, but as a GM I think I will frag the troll and his bins if Ex-explosive AR ammo rounds 
I figure the balance part is covered by Metahuman Customization having to effectively completely redesign the grip and trigger area and putting more weight back on that end. Plus, remember, they still
do get a -1 penalty, so it's not like they get off scott free for doing it.
Secondly, my Troll uses APDS, not ExEx. His weapon is also Suppressed and has Electronic Firing. Caseless ammo, -9 to hear the shot, and no rifling on the bullets if/when they're recovered, because the disposable Sabot got the rifle pattern, and was destroyed as it exited the barrel. Very useful for a guy whose job description includes spraying vast amounts of lead.
Plus, if you do it that way, you only have to get each gun up to 5 points of recoil, which is
much easier than 9, and you can fire two Long Bursts, one with each gun.