Wow, you obviously have no idea what you are talking about. Based on past precedent regarding conflicts, or potential conflicts, between the US constitution and a states constitution, the federal courts virtually HAVE to take the cases, and in the event that the state wins in the first round, appeals being granted is a given until it is in the Supreme Court.
The question of whether state constitutions can supersede the federal constitution based on the states rights argument was settled years ago. Several states constitutions specifically precluded women and blacks from voting. Guess what? Women and blacks can vote in every state. The Us supreme court struck down the constitutional provisions of those states that singled out white males as the only eligible voters.
"States rights" do not apply in cases where a state constitution potentially violates the Federal constitution, since a state does not have the right to violate the federal constitution regardless of how they do it.
Hard to overturn? In order fro the gays to win, they have to get ONE single, solitary federal judge in each district to rule on their side. In order for the fundies to win, they have to win every appeal right up to the supreme court, have to win in the supreme court, and have to prove what is basically impossible, that banning gay marriage is somehow not a constitutional violation.
This is why Bush was pushing for a federal constitutional amendment. Constitutional amendments at the state level simply will not get the job done since they will be overturned in federal court as violating the US constitution. And there is really no doubt that it violates the US constitution, or he would have simply pushed a law through congress. The support for such a law was there, and congress would have had the jurisdiction to pass such a law based on the fact that the status of gays regarding marriage significantly impacts insurance, health care, banking, and even taxation, which certainly puts it under the category of "interstate commerce".
That did not pass a law because they could not find a single reputable legal expert who was willing to claim that such a law was constitutional.