As I have expressed before, I think the SCOTUS should allow for this sort of behavior, because it's constitutional. It's not a lack of backbone; it's the fact that there's simply really not anything in the Constitution that actually prohibits partisan gerrymandering, as much as I wish there was.
I want to try to make my position clear. I don't like partisan gerrymandering. It's bad. I want it gone and would be in complete support for a law or constitutional amendment or law to to end the practice. Congress indeed has the power to do so, at least for House of Representatives elections (to end gerrymandering in state legislatures, one would require a constitutional amendment).
Nevertheless, I also am forced to recognize that it's an issue to be solved by the legislature, not the courts, simply on the fact it's constitutional (this is exactly why people's ire should be on the legislatures on this matter rather than the courts). It is entirely possible for something to be both stupid and constitutional, or bad and constitutional, or evil and constitutional (slavery in the United States was a far greater evil than gerrymandering ever was, and it was constitutional for about 80 years). Thus despite my distaste of the practice of gerrymandering, I think they were absolutely correct in affirming partisan gerrymandering as constitutional. As for this specific case, this was indeed partisan gerrymandering rather than a racial gerrymander (in both states), despite some weak attempts by some to argue otherwise--they're indeed some of the most blatant partisan gerrymanders I've seen. Thus I believe SCOTUS was correct to allow both Texas and California to do this, and other states.
I will, however, agree that the arguments of trying to claim there's inconsistency between Democrats criticizing gerrymandering and engaging in it doesn't make that much sense, because someone really has to do it to remain competitive in politics if the other side is doing it, especially when to the extreme Texas is doing so. It is entirely possible to dislike the rules and try to change them but, as long as they're around, still use them (it's like if a sports player thinks something should be banned from competition--it isn't consistent to still use whatever it is, because it's still in the game and you just give yourself a major disadvantage).
Though as long as I'm staking out my position, I would also add that I'm not very fond of the "California put it up to the voters, but Texas didn't!" talking point, at least how it is frequently expressed. The problem is that the Californian government likely did not do this out of any kind of moral obligation to put it before the voters, but because of the legal obligation. Unless there's actual evidence that California would have done it via referendum even if it wasn't required to do so, then there isn't too much moral high ground to be taken there.