I don't want to put words in the guy's mouth, but he seemed pretty clear that he believes these advantages don't really exist:
1) Beta testers need to actually know what they are talking about and be prepared to test a game at a stage where it is essentially not playable. 99% of open Beta testers don't and won't.
2) Beta players need to actually be willing to do the work to comprehensively test the game, which means doing it under directions, not just randomly bashing around.
Basically, if Paradox ran an open, paid-for beta for this game 99% of the reports would be "WTF Paradox I paid real money for this and its unplayable! And where the $%^& are the NATO counters etc.etc.etc.". Any useful feedback would be drowned out by this kind of moaning, rendering it useless.
I agree that HoI4 isn't the ideal candidate for an early access game, not least because, as Johan said, they don't need the funding the same way that indie devs might, etc.
Disregarding all of early access, though, is a little drastic, at least to me, which is why I preferred podcat's post over Johan's~ I've paid for a couple early access games, and I haven't been disappointed yet, because I knew what I was getting into, I did my research into what state the game was in, and I wanted above all to support the devs and see the game finished, even if I couldn't play it (and enjoy it) immediately.
As for the negative comments, I guess you'd have to ask other devs who have used early access how they deal with it. Paradox doesn't seem to be crippling under the weight of all the negative feedback on completed games, though, hah!
(that last part is a joke)