Grease is a heavy duty lube. Used on things that are under a high load, lots of weight, lots of force, maybe lots of heat. And it will still fail, at times.
I use grease on three (types) of rifles. M1 Garand, M1A and SIG556R - in areas where it doesn't get very dirty very fast and will last through more than a couple/three shooting sessions. The whole purpose of grease on the M1 Garand was due to heavy/heavy/heavy rains washing the originally prescribed oil in the Pacific islands.
I just oil. While I may use more than a lot of people (a drop here and a drop there but I clean/lube more often than many people) I don't have malfunctions from lack of lube, nor from too much lube, nor do I find rust inside/outside my guns.
The grease you found inside your pistols was probably more of a preservative seen on some guns shipped from the factory designed to protect the internals from rust/corrosion during shipping/storage prior to sales to customers. Most everyone here recommends cleaning/lubing a new pistol prior to going to the range as that preservative stuff isn't a really good lubricant.