In the off-chance you end up depending on that legacy code, repackaging that one or two dependencies shouldn't be that big of a deal.
Probably the biggest stragglers will be build scripts, and as recently as mid-2020, the answer to "how do I build distributable artifacts without using setup.py" was still "you can do it but there's no good definitive answer": https://stackoverflow.com/q/58753970/467366
There's also been a lot of mixed messaging in this space, so I think there's a decent population of people who think that the way to stop invoking setup.py is to stop using setuptools entirely, mixing up "don't invoke setup.py" with "use a backend that doesn't have a setup.py".
But you are right to say that this has gotten a lot better over time and the word is slowly getting out.
I did always find the setup.py approach misguided for several reasons, so it's more of a casual observation I've done that I thankfully rarely encounter it these days.