Ideally, all the benefits that come from marriage would be either eliminated or made non-exclusive to marriage and relationships. However, given the current situation, expanding the definition of marriage is a good stepand can even lead to a more ideal situation.
It’s basically ideal versus non-ideal theory. Should the legal institution of marriage, and especially how there are special rights attached to it and pretty much only to it, be a thing, even now that it has been extended a bit? Probably not. Given the fact that legal marriage is currently a thing, is it currently more beneficial to expand it, and does that expansion even signficantly limit facilitating that ideal? Yes, and in fact it sets a precendent for the ideal.
What will be a problem is, first, people chipping away at the ruling–as with the ACA and Roe v. Wade–and, even more certainly, people (including cis gays) thinking that the struggle is over and leaving multiply marginalized queer people (especially trans women) out in the cold. Both of these things are already happening.
The war is not over. Just one battle, a comparatively easy battle, and that took considerably longer than I’ve been alive. Thirty years, given a conservative estimate. I would rather not have all the other battles take so long, or have all the troops leave but the vanguard.