Fit is important, anyonethat says no they are off their rocker PLAIN ND SIMPLE
This may ramble a bit, just woke up, working midnights.
Fit matters, just way less then most people think. You need to be able to reach the operating controls, but beyond the trigger stroke, most of the controls are secondary. I don't know many shooters who can reach mag releases on most handguns without "rolling" the grip. For myself, the only handguns that I can operate mag releases on, without moving my firing hand, are those with ambi mag releases. Does this mean all i shoot is a revolver, since these other handguns don't fit properly? Of course not. I'd love to have longer thumbs, but thats not gonna happen.
Personally i find pistols that are too small a much larger handicap then ones that are too large. IE, it's much easier to fire a Mk 23, a pistol that fits no one I've ever met due to it's frame size, then a baby browning, on which i can reach all the controls.
Some aspects of construction will add challenge to the shooting. Sigs have a high bore axis. hence recoil is accentuated over a similar pistol with a lower frame/barrel relationship. They have a long DA pull and a deep frame front to back, this limits use based on hand size as it's hard to run the trigger straight back if you can't get enough finger on the trigger.
On the other hand, take a glock trigger, yeah, out of the box they fell crappy. This isn't a fit issue. it's just feel/perception. I have yet to meet an adult who can't place a finger properly on a glock/M&P trigger and run it without canting or torquing the pistol once they get used to the feel. I have met lots of folk who won't put the time in to learn though because they won't work past the feel, NOT the fit.
Finally take a 1911, the one big advantage to the platform? 3 lengths of trigger, and no take up and a short stroke. Pretty much anyone can shoot a 1911 well....ok, unless the slide lock is extended, and the saftey somewhat enlarged over the GI size, most find the controls awkward initially. But because we're told it's the perfect pistol, we decide it must be us and learn to get used to them. But it is a platform that is easy to shoot, hence it's use in the past as a bullseye gun in center fire categories.
Feel is subjective to the individual, fit is mechanical, and based on geometry. I think in this discussion there is a certain blur between the two..All this being said, fit make a pistol easier to shoot, but all the fit in the world won't let you shoot well if, as Metcalfe so perfectly puts it "Align the sights and press the trigger straight to the rear.
Do that with any pistol or revolver and no matter how it feels in your hand, your hits will be on target."