Yes, there is a loss of gas at the cylinder gap.
See the flash?
That's why you don't want your hand THERE. But as said, the revolver was designed around that. Two identical .38 Specials- one fired in a revolver, one fired in single shot pistol, such as a Contender, the single WILL get more energy.
The comment is rather boneheaded, since I fail to see .460s, 500 S&Ws as a "weak" cartridge.
BTW, I notice there is a measurable space between the cylinder rings and cylinder walls in the engine of my truck. Using his logic, that will run only poorly and weakly.