You're mixing issues. Bikes are below weight for a reason, and the weight limit has a reason too and this eats into both of those and puts feedback pressure on both of those, but gaming a system is a different thing from what is fundamentally better (allows you to ride faster, where crashing counts as much slower, possibly permanently). As for gaming the system, if some configuration clearly has advantage relative to the rules, then everyone will use it, and it won't be an advantage to anyone. A brake is as much a performance device as a safety device. A bike without brakes is perfectly safe for me, because I won't ride it over 5mph, with my feet dragging the ground at that. So, my brain is the safety device. The brake is what let's me go fast.