Not really, but that's what Mother Jones wants you to believe. With "Supreme Court Upholds Pension Gender Gap" as a headline, they want to send the signal that the Supreme Court has considered the existence of a gender gap in who receives how much of a pension and deemed it just fine. That suggests the view that what the Supreme Court is about is results. We should evaluate them according to whether they decided cases that give us the right results. Several justices on the Supreme Court might be happy about such a description, but I'm sure that at least four of the seven justices in the majority in this decision would not, and I'd guess that most or all of the other justices would not approve of such a description (even if I happen to think it's true of some of them).
If you read the article, it actually undoes a lot of the damage from the headline. Authors of op-eds don't usually choose their own headlines, and I'm guessing that's what happened here, so I'm not blaming the author, whose article is largely accurate and doesn't really spin the facts too significantly. The issue before the court involved a 1978 law that makes it illegal to discriminate against women who take maternity leave when counting pension benefits, because standard practice at the time was not to count maternity leaves as time served when calculating how many years someone worked for the company. That law counted such a practice as discrimination, and it made it illegal to ignore the time a woman was not working if the reason was maternity leave.
The issue before the court was whether a maternity leave that occurred before that law was passed was similarly affected. The majority ruled 7-2 that the law was not retroactive, and thus when it was passed it did not suddenly pass on the features of future maternity leaves to past ones. In other words, it is not illegal now not to count the maternity leaves before this practice counted as discriminatory, but it is illegal now not to count the maternity leaves after the laws was passed.
So the majority ruled in this case that the law that makes this kind of discrimination illegal wasn't a retroactive law, i.e. it didn't make what people had done before the law was passed suddenly criminal when it had been legal before that. It also treated the discrimination the law prevents as occurring when the maternity leave was taken, not when the pension benefits are calculated. I haven't had time to research the law itself or the claims of either side in how to interpret it. I'm certainly open to Justice Ginsburg's dissenting argument that the majority interpreted the law wrongly. In fact, I'd probably lean that way just from what I've read in several accounts. I'd be a little surprised if the law was narrowly about how a company counts maternity leaves at the time they occur rather than about how a company should count previous ones when it calculates benefits much later. So if I had to guess my view on the legal question, I'd predict that I'd have strong inclinations to hear out Justice Ginsburg's argument, since it seems more likely to be correct from what I've seen.
This isn't to say that I agree with that as a policy matter. There are two kinds of fairness at odds here, fairness of outcome and fairness of granting someone credit only for what they contribute to the company. If you begin with a socialist conception of justice, you would consider any inequality of outcome to be unfair and immoral. On the other hand, a libertarian conception of justice would consider such a view to amount to stealing from those who actually contributed to the company for all the hours being counted in their favor. It may be unfair on one level that women can't help having to take time off from work for maternity leave, but it's also unfair on a differently level to count that time as work time when someone else actually put in more time working for the company and didn't get to have time off count. One might see that as discriminating in favor of women who take maternity leave against those who don't (including women and men). If all you care about is the just result, your views on such matters will enter in to the calculation of whether this outcome is just. One can take either view on that matter and still decide this case either way. (And I want to say that those views aren't mutually exclusive. You might think both kinds of justice are morally important. I in fact do, and I'm not sure how I'd sort that out in this kind of case. I would be open to being convinced by policy arguments either way if I were in Congress debating such a law.)
If the justices were using such considerations, I think a stronger case could be made that they simply upheld the gender gap. But the reasoning they actually gave was about legal matters. As I said, I might actually lean in the opposite direction on those legal matters (even if as a policy matter I think a case can be made either way in terms of whether we should have such a law to begin with). Nevertheless, it strikes me as strongly misleading to say this decision upholds the pension gender gap, for several reasons.