I understand that not having a dedicated IT staff is no excuse for not buying the appropriate tool for the job. If you can figure out how to install CAD software you can figure out what the word "Home" means on the Windows 10 "Home" version and can opt to buy the Professional version pre-installed instead. It's not like anyone will be installing it themselves.
And if this is so mind-bogglingly complicated then the company is precisely the type who should be forced to install Windows Updates.
Also you're right, it isn't just a concern with the home edition. In fact it's not a "concern" at all. Not updating security holes is frankly stupid. Deferring them with good reason is okay, but no updating security holes is frankly stupid.
I feel like saying frankly stupid one more time.
Oh maybe you have a good reason due to an application incompatibility. Well the deferral process gives you time to sort that out after which not patching your security holes is ... frankly stupid.