Your right, lag time might not be as detectable in a pistol as in a rifle. But especially for people who are one handed pistol shooters, there's definitely a lag between the time that the finger reaches for and releases the trigger and the bullet exits the barrel. Maybe there's not that much of a difference in time, but there's a difference in the balance of the gun that affects muzzle stability and holdability during "the event". It happens in a flash, the gun moves as the trigger is released before the boom even starts, no man can hold a gun rock steady. It's at that point, that the faster the bullet exits and the steadier the muzzle can be held, accuracy results.
I know a fellow air pistol shooter who bought a device that's comprised of a sensor that attaches to the grip, and which is wired to a computer screen & program. It simulates and records all of the muzzle movement on the computer screen starting just prior to releasing the trigger, and then records everything up until the projected impact of the "make believe" projectile, all based on the motion of the sensor. That's really when the lag time really starts, and the longer the barrel, the tougher it can be to keep the gun steady during the entire process.
One second the sights are seemingly on the bullseye, then in the next millisecond, the brain tries to release the trigger while holding the gun steady. Air pistols have a relatively long barrel and lag time, and guns with much heavier triggers make it even that much more difficult to shoot while holding steady. So, maybe it's not classic lag time due to waiting for the bullet to exit the muzzle, but the extended lag time waiting for the completion of "the entire event" and trying to control it.
It's mostly about isolating the trigger, and not pushing the muzzle away from the bullseye while releasing the trigger. And these air pistols have very ergonomic, anatomical grips. It's shooting that involves a lot of follow through after the shot, with a velocity of about 550 feet per second. .22lr pistol shooting is similar too, trying to control the muzzle of a 5.5 inch barrel versus a 7.25 inch barrel, especially with one hand. I've shot both models, and controlling each while shooting one handed is very different. The longer one is more resistent to recoil while firing, but keeping it steady while releasing the trigger is tougher, for me anyway. Even the famous S&W Model 41 target .22 comes with either a long barrel or a shorter, heavier target barrel that most target shooters use. And when a red dot scope is mounted on a pistol, each movement becomes illuminated and visible to the shooter. Sometimes the best any shooter can do is to hold the sights to moving around in the target black and trying to shoot into that area, rather than to try to hold them perfectly steady enough to shoot a perfect bullseye. So the overall holdability of the pistol is really important too.
In theory, the muzzle is usually moving away from the bullseye as the trigger is pulled due to hand movement, and so the faster the bullet exits the barrel, the closer the bullet will impact to the point of aim, if all else was equal, which it's not. It might be different for benchrest shooters, and sights, inherant gun accuracy, barrel weight, trigger pull weight etc.... will always be aditional factors contributing to overall shooting accruacy.