As a self-hoster for over a decade, setting up SPF, DKIM, and DMARC are pretty much once-and-done and free, so there's pretty much no downside. I'd be shocked if most self-hosters haven't set these up long ago.
I don't know if self hosted but I regularly get emails from companies where this has not been set up. And not "Joe's Car Detailing" but rather "medium size gas provider" ...
Word, the truly hard part of self-hosting is IP warming, and fill out those dame form to FANNG to get white listed, it is a rabbit hole that take forever with no end.
For sending outgoing emails in a self-hosted environment, the toughest step will absolutely be to find a host willing to accept you as a customer.
A lot of places don't accept outgoing SMTP traffic at all, some allow it for personal usage and finding someone who accepts you sending lots of outgoing SMTP traffic is gonna be really hard, except if that host already hosts lots of already spam-marked IPs.