Yes, "domain authority" is a useless, made-up metric. The theory behind domain authority is that a page put on a "high DA" domain will automatically rank well in the search engine results because it's on a "high DA" domain. It's doesn't work that way.
A good example would be links that I have from a prominent .EDU (University) site in Texas. I volunteer to speak regularly with an internet marketing class every semester. The professor has me in as a guest speaker. He links to my site on his class page. That page is so buried, very deep, on the EDU site. It would be difficult to find it from the site's home page. It may not even be linked from the rest of the site, it may be just a page on the EDU site. That link to my site means nothing, doesn't help me in any way at all. If there's something called "Domain Authority", then my site would have benefited and I'd see increase rankings. Nope. Nothing.
Domain Authority can also be easily faked and manipulated. People are manipulating Domain Authority so they can sell links to you and sell "high DA" domains.