We do pretty good on Siteimprove and similar checkers although these are frequently wrong and in some cases I think think the specs are actually wrong or miss important things for political reasons. We have customers who send us bug reports and we fix them, we catch others preemptively ourselves.

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.