Yes, but, legally speaking, an adoption, while unequal, is still very useful.
I have friends who adopted each other before marriage equality was a thing in Washington state. And the thing with adoption, that isn’t true with marriage, is that it literally lasts until someone dies. My adoptive parents still have legal visitation rights even we completely disown each other. They’d still be my next of kin, and my genetic mother would still not be allowed visitation rights etc, unless specified in the will.
So, for all intents and purposes, adoption is an even stronger system than marriage, because it’s not technically a contract but a covenant with the government, depending on the state. There’s no legal way to reverse my adoption (closed adoption, initiated in 1989), so it may possibly be even more valuable than a marriage anyway, if we’re coming from a strictly utilitarian perspective. I’m still very happy about marriage equality. I’m just saying that adoption is an even stronger option, if you want to choose something absolutely irreversible in some states.