> ...but there's nothing to "fix", it works as intended
If there were nothing to fix, they wouldn't be telling people not to start new projects with Moment. They actually do mention a few significant issues that they can't / won't fix in Moment such as bundle size and mutability.
I will concede that perhaps Moment was "done" at some point before, some years back. When it was quite complete, yet was still the best way to do reliably work with timezoned dates in JS. But as Intl support improved, and better designed alternatives grew, it got rather obsolete, and will get more obsolete over time.
jQuery for comparison, while largely obsolete for rich web app development, is still very relevant to ecommerce, website-development-for-hire and other niches, and it will probably stay that way for a long time because it's the right design for those problems. Moment isn't the right design for any problem anymore, unless, as the article says, you need to support old browsers.