I saw that video a while ago. With modern self defense ammo, there's not much difference between the typical service calibers with regard to terminal ballistics. They all seem to work about the same in real encounters.
I think for most people choosing a semi-auto for self defense, 9mm makes the most sense. Relatively lower recoil, cheaper practice, and more rounds (may not be much of a difference with single-stack guns). Even someone who's very skilled with a .45ACP pistol will be able to get accurate rounds on target faster with a 9mm, given the same platform*.
Does that make the .45ACP a poor choice? Of course not. It's still a very effective round, and those who choose to carry it (or .40S&W, or .357SIG) will be well served, presuming they can shoot it well and it's reliable in their gun of choice. But at the same time it ends up being a case of diminishing returns, which I believe is the point he was trying to make in the video. Does the .45ACP's attributes really outweight the 9mm's attributes enough to justify it as a self defense gun? To me, not really. To someone else, maybe it does. It's nice to have choices so we can each choose what works best for us.
And I say this as someone who has a Beretta 92FS as a HD gun, which many say is too big for its caliber, and someone who thinks the Sig P239 in 9mm makes for an excellent carry gun despite critics saying it's also too big for its caliber.
As for Yankee Marshal himself, I do watch his videos from time to time, keeping in mind that he is basically just sharing his opinion on the topic at hand.
* OMG...did i really say "platform"...?!