if they run hardware that’s not cutting edge, by all means, that’s the best solution as a first distro.
ubuntu is important as a stepping stone. myself and everyone I know that’s on Fedora et al started with Ubuntu. we learned what’s what and how to go about doing things and after hitting the ceiling one too many times, we tried other stuff, found better havens and finally abandoned it forever.
so I’d caution against any action aimed at hurting it. leave it be and know that it’s still the most user-friendly solution out there and the one that’s most likely to “just work” for most people. it’ll convert people over, whether from Windows or MacOS. once they’ve crossed over, they’re more likely to wander further.