If you were to ask a full scale designer about chassis flex they would say it is bad. But they have hours in simulators and sophisticated suspension designs to over come compliance problems. As racers we have very little time to absolutely dial in the ultimate set up and rather old fashioned suspension design so we can use chassis flex to help. We can be 1lb out on the spring 20 cst out on the oil 0.5mm out on the position of the shock for the ideal configuration, but chassis flex will overcome all that and get a car that we can drive around the track in the quickest possible way.

So, chassis flex is bad but it is a compromise and a way of achieving balance easily.

An interesting point is that now MotoGP are talking about bike frame flex...so maybe someone is looking at RC