Should they also be forbidden from using Linux, Windows, macOS because it allows for the same exploit? Should everyone on the world be limited to iOS and ONLY iOS which is limited to ONLY apps (and soon media content) Apple allows you to use?
You joke, but this is exactly why I recommend Macs or iPads to all of my elderly friends and family. Trying to run Windows safely turns into a level of knowledge that my 75 year old mom isn't able to do.
I don't yet know of a good alternative. I desperately want one because Apple kit is expensive. But for now "$500 for an iPad" is the advice that gets me the fewest calls for support.
My grandma does three things on the Internet: talks to her family on facebook messenger, receives photos in email, and checks her stocks on ameritrade. So yes, with those requirements, she should only use iOS.