It's not enough. I have a domain that I had a very long time but it is on an undesirable tld. I got it long before it was problematic. Outlook always puts my mail in the SPAM folder even though I have done everything I could. I even deliver through a trusted provider. Not on any spam list. DMARC, DKIM, SPF all set up. No dice.

I've never had a problem not having dmarc. DMARC doesn't really mean anything. The security comes from DKIM (or SPF, but that's garbage)