Most people will never make it through a lengthy SHTF. Worrying about whether your sidearm is the "right one" is silly and makes it easy to make fun of preppers. Is it not a valid concern? Sure. Is it even in the top 10 issues to worry about? No.The idea in the OP video is that common hardware in a common caliber makes logistics simpler (more easily supplied, serviced, modified, resupplied, supported, etc.) than uncommon hipster Gucci hardware in a less common caliber.
Such support will likely be more difficult in a lengthy SHTF scenario, and thus this criteria may be more advantageous than it is during normal times. Pretty simple straightforward stuff.