The idea of the unreliable part - sorry not to be clear - was that the light might make the slide heavier and interfer with a clear, crisp stroke for pump guns.
Some folks have trouble with short stroking the gun and if not familar, might get into difficulty.
The debate about whether one should have light on a gun is independent of the type of gun as far as tactics. See in the dark vs. pointing out where you are vs. having to point a gun at innocents to see what's up vs. chance of an ND when manipulating the light - quite a lot to think about.
But I was thinking about the old click, ching-ching screw up. You know many recommend Grandma with arthritis MUST use a 12 gauge - ENUF SAID!
So making the gun heavier and the slide harder to slide - seems a plan.
As far as the Judge - Tom wrote a rather complete analysis of the Judge for SWAT. Wasn't that positive. But I know lots of unskilled folk who think they are Mjolnir (just saw Thor). Ultimate stopper than you don't have to aim.