It's an interesting argument. The fact this article exists is somewhat proof that it is a differentiator. The flipside, however, is that spammers very specifically require their emails to get to add many mailboxes as possible, so their motivation is greater to make their emails service compatible.

Company sys admins have likely got all sorts of other issues to worry about, and the occasional report of an email not getting through is likely low on their to-investigate list.

Having said that, I self host a mail server, and have all those things setup correctly, and my workplace uses Outlook, and I've not had issues with delivery, so it's not a particularly difficult bar to jump.

What? How does it prove it's a differentiator for someone who wants to be a spammer, which is what the comment you replied to made a claim about? As far as I can tell, it's evidence (not proof) that Microsoft thinks that they will reduce spam by requiring it, which in turn is circumstantial evidence (definitely not proof) that spammers might have to spend some amount of effort to start using DMARC. I don't understand how you can conclude that it would be onerous for them to do so indefinitely; it seems equally plausible that they might have just not bothered to do it before now but will be able to start doing it without much cost.