Hi @davidbourguignon ; welcome to the /e/ Community!
So…to directly answer your question, Zorin is pretty good, and Linux Mint is also pretty good; GalliumOS might be worth a look for Chromebooks; it’s optimized for them and keeps the F-Key functionality intact, most notably.
That being said…it sounds like you’re “in the trenches” and have experience specifically with this sort of work, but I’d submit that there is, at least in my opinion, a fundamental difference between the Android->/e/OS migration and the Windows->Linux migration: everything else.
Amongst the reasons I use /e/OS, instead of PostMarketOS or UbuntuTouch, is because a huge amount of /e/OS’s development time goes into making the shift from Google to Murena as smooth as possible. A handful of Android apps don’t work, but well over 99% of them do. Apps come from the App Lounge and/or Aurora, which is pretty much a drop-in replacement for the Play Store (with less spam as a bonus).
While some users don’t really need Windows because they do pretty much everything in a browser, I submit that a good number of them have already moved to a Mac or a Chromebook or just doing everything on their phone. Some more of them may be fine using LibreOffice, or may need one or two other programs for which there are drop-in replacements, but there are a good number of Windows users who are still using Windows, intentionally, because of the long-tail of applications available for the platform. Yes, the “Word and the Internet” crowd would probably be fine with LibrOffice on Zorin, but there are a whole lot of musicians for whom Ableton is a must-have. iPhone users don’t have the sort of device backup and management functions available to them on iTunes or iMazing.
This isn’t an argument against moving people away from Windows, but it is an argument that there are intermediate steps. /e/OS is an easy move away from Android because it is Android, with great care to make sure that if someone wants Android-but-without-Google, the only thing they’re giving up is the Google. Neither Zorin nor Mint nor Ubuntu nor Oracle Linux are going to give users the same ability to keep their existing software library and workflows and limit their replacement to the OS. Now again, for some people with very limited workflows, it’d be super easy to move them to Zorin, and the fact that your shop exists is proof that it can be done. However, I would submit that it is well worth assessing a users’ needs before causing a support headache that may not be possible to migrate.
Hope it helps!