That you should have a purpose built semi automatic magazine fed rifle vs a hunting or old milsurp type rifle for defense is valid. The sole valid reason I can see for not taking this course of action is if you simply cannot afford modern defensive weapons and need to rely on basic guns. A guy with this sort of rifle is going to lean heavily on his pump shotgun (250 rounds of 12 gauge 00 buck for $125)
I fundamentally disagree with the approach listed in the video that you should buy a magazine fed rifle, a pump shotgun then a semi automatic mag fed pistol. To his credit Maine Prepper says you need to worry about the specifics of your scenario as well as scenarios you might envision. That valid point aside a semi automatic rifle is by far the most expensive rifle to purchase and equip of the three. Also they are not concealable and are a one trick pony. Granted it is a good trick but there is still a lack of versatility and concealability. These factors make makes me think most people would, albeit temporarily till they can save some more funds, be far better off with a nice handgun like a Glock 19 and a pump shotgun than a rifle like an AR-15. To me that two gun combo is going to fare better over a variety of different scenarios than one single rifle. Granted you should get all three as soon as it is practical.
Anyway those are my thoughts. Hope you enjoy the video.