Day.js is basically a drop in replacement, and is 97% smaller. You still need to regression test, but imho it's one of the highest impact ways to spend a few hours if you care at all about performance.
Yep, indeed there are ways to migrate, but it's not necessarily easy. For instance in my last project, we used moment-timezone, and integrated other libraries such as https://github.com/urish/ngx-moment to format date/times in component templates. Of course it's possible to move away from that, but it would take time away from more useful work.
Ya, but testing dates and times is very hard. It’s easy to miss something.
True. But in this case the regression testing is mainly for if you miss an import, since some of the formatters require plugins. Fortunately if that happens it will be fairly obvious since iirc there will be random letters in the middle of the time string.