RE: aluminum parts vs plastic parts
Racers don't want flex, they want stiffness. Aluminum means less 'slop', it means faster recovery or righting of the vehicle, better repeatability or consistency in handling, etc. Graphite and carbon fiber are also favored for the same reason. The stiffer parts are more brittle, they break easier, but racers, at least experienced racers, are willing to sacrifice durability for getting a slight advantage over their peers.