Last spring ran into (no that isn't the reason for his retirement) Thomas Grandi off the poma at Lake Louise. He was in his race boots and skiing bumps not badly for a retired racer. Which is to say I would have bet on him in a bump competition.
Last spring Bill Keenan (ex-80s bump champion) stopped into the store for a pair of skis. Again he skis a stiff boot all over the mountain and voiced his dislike for soft boots that left him without enough support in changing situations.
Two years ago skied with technical director of Fernie who for the first time in his career was skiing a plug boot (Dobermann). He was amazed at the difference in control.
There are however members of this forum that ski very soft touring boots.
So what is right? Whatever works for you.
Purpose of stiff boot in my opinion ( stiff longitudinally, laterally is another matter, all boots benefit from lateral stiffness) is more to help hold us up rather than to transmit forces to the tip.
So how much help do you need for the way you ski to support your out of balance movements?
The more you can maintain balance without relying on the boot for support the softer your boot can be if you like. It is all about your ability to maintain balance. That is a function of ramp, binding position and cuff alignment coupled with the diversity of terrain and your aggressiveness.
A boot can only be too soft or to firm for you.