1) The weight of discs vs rim brakes have no bearing on UCI permitted bikes. The bikes have a minimum weight that is far higher than the any 4 ounce difference between disc or rim will make.
2) If not subject UCI or any racing organization, why do you care what others think is right for them? If they are competing, then it will still be the person that crosses the line first. And more than the "best" brake type goes into getting one over the line first.