WCAG is lot lot more than just using <dialog> and unless you do a thorough review with a professional in this field, <dialog> won't solve anything. Do you know how many other WCAG guidelines your app or your site misses. No one knows that.
It is a problem that the experiences of disabled people are erased by the current regime, I haven't once seen an organization actually ask a disabled person if they can use the site or how it can be better.
Also I think accessibility tools are trash. If I start NVDA on my dev machine I have to power cycle it to get control back. Microsoft Narrator sorta works but the more you use landmarks and other aria-markup the more it starts blurting out things like "LANDMARK NAVIGATION LANDMARK!" in the middle of reading something even thought Siteimprove thinks it is all peachy. Is it a fail? Or did the tool fail? My tester or myself can look at an application as a sighted user and test it in Firefox/Chrome/Safari and say "it works" but it is not clear at all what the "definition is done" for testing with screen readers.
I hear JAWS is better than the others but it costs about as much as a car. In the meantime though I know when we don't use <dialog> we fail and I've seen a lot of third party modals that don't use <dialog> that all fail.