Rusty, let me try.
-is a gun with 18 parts better than a gun with 36?
Is it better? Maybe, maybe not. It would be less prone to breakage of parts and therefore more reliable ALL OTHER THINGS BEING EQUAL.
-does fewer parts mean that you will have fewer parts breaking?
Yes, ALL OTHER THINGS BEING EQUAL.
-does fewer parts mean more reliable?
No. What if you had a gun with 10 parts and another with 100 parts that was on par with a fine Swiss watch. If the gun with 10 parts wouldn't feed or the firing pin was of such poor quality that it broke every 5 rounds and the other gun would feed anything and had a firing pin that would go 100,000 rounds then the statement would not be true, but all other things would not be equal
-is less more?
It can be.
With two guns of equal quality and functional reliablity, the gun with fewer parts would be less prone to breakage and therefore more mechanically reliable.