There seems to be a confusion between lightning fast actions and being able to play lightning fast...

Watch any concert pianist, and it's obvious that lightning fast passages are possible on VERY heavy actions. The thing that weight gives you is not speed, but precision of dynamics. It is VERY hard to dial in volume differences when you can barely feel the action at all. This may account for many arranger demos I hear where the player is having a hard time playing an entire line at one dynamic (or thereabouts). Horns, strings, winds, all of these things need lines that don't jump from note to note (unless that is a specific effect you are going for). The lighter the action, unless you are playing hard enough to keep it at close to the top (which ain't how horn and string players play!), the tougher it is to feel those subtle differences between mp and mf, for instance. And with modern arranger sample sets, those can often sound quite different.

One of the most telling audio things is the guitar patches with the 'hammer-on' velocity triggered sound. I have rarely ever heard anyone using one of those on a lightweight that doesn't get it when they DON'T want it as well as when they do.

Weight of the action is far more important than many think....