Good point.
I guess my point is that I believe the Court may have been in error in not striking down Section 2.
Once Congress arrogates this power to itself, what is to keep it from deciding that custody decisions, divorces, etc. by one state need not be respected by others?
The point is moot, of course, since the present, and probably any future, Congress would not pass a DOMA. In fact, they are more likely to pass a law requiring every state to accept any marriage legal in another state. Which, if you accept the constitutionality of Section 2, seems well within their power.
Note that one of the reasons that we have to question what Congress might do is because state lawmakers foolishly ratified the ill-conceived 17th Amendment. Otherwise the state legislators could better rely on the Senate to kill legislation such as you mentioned from being passed.
Otherwise, patriots need to support conservatives trying to get themselves elected to Congress so that Congress can impeach activist justices.
Finally, the states need to learn how to amend the Constitution again so that they can do so to tighten the "leash" on Congress's limited powers when they need to.