You said Alito/Thomas is saying Texas has automatic standing. I don't believe that to be the case. The long standing position of Alito/Thomas is that because the Constitution says that the Supreme court shall have jurisdiction in cases between two states, the Court cannot reject a petition in such a case, for any reason. The petition must be granted. Period.
It is only after the motion to file has been granted that the Court can deny relief on a basis such as lack of standing. (Although previous opinions by Alito indicate that he believes there has to at least be an allegation of harm in order to meet the requirement of "controversies" between states.)
Alito/Thomas don't say why they would have not granted relief. But considering that they did not dissent, and made no mention of the standing issue, and did not write a longer opinion as they have done when they dissented, it is reasonable to conclude that they agreed with the issue on standing.
That is, they believed that the Court should grant the motion to file, AND THEN deny relief due to lack of standing. But, as I said, that is conjecture because they don't actually say why they would not have granted relief, so it could have been standing, laches, failure to state a claim, insufficient evidence, relief request not warranted or possible, or whatever. But it looks like they agreed with the lack of standing issue considering that they agreed with the majority.
Note that Alito/Thomas did not dissent. They merely made a statement. That implies that they agree with the decision, but simply feel it should have been denied on the complaint rather than on the motion to file.