I own 2 Amps, the Monster truck, and the Buggy. Have had them for 4 years.
I upgraded the MT's arms to RPM, and left the Buggys arms stock.
I have never broken an A arm on either vehicle. And both have good brushless motors and go around 35mph.
I've bashed em hard on all surfaces, raced them, and even taken them to a skate park and jumped them 20+ feet high.
Honestly if you're breaking Arms left and right I would have to say you are just a poor driver unfortunately.
Driving these trucks on the stock motors is pretty tame, and on a stock Dynamite brushed motor aside from very bad luck - you have nowhere near enough power or speed to break a Arm.
With that being said you either have the worst luck ever... or upgraded your truck to a motor you simply can't handle. Or - you can actually drive well.. and just don't care.
As for the aluminum Arms. Stay away. Especially if you're already breaking Arms constantly. They're expensive, and they will bend. Save the aluminum parts for wheel linkage, knuckles, hubs, etc... nothing big that will add weight or bend.