Sure, but for me the standard isn't whether it's visually realistic. Plenty of good stuff isn't particularly realistic. Traditional Chinese landscapes aren't realistic, but a lot of them are great. David Hockney has a lot of good work that isn't realistic and uses primitive-looking technique. The standard is not realism or which style was used. The standard, for me, is whether the artist was any good at art. Hockney is. (Usually.)

I'm not particularly basing my opinion on the examples in this article. It's easy to see that a lot of surviving European medieval art sucks. Maybe "surviving" is the problem. Maybe the good stuff got all smokey from being displayed and only the leftovers and student paintings, in storage, have survived.

On illustrations, everybody can see the difference between Durer and most medieval stuff. It's not simply style or taste.