I think it’s hard to describe medieval in terms of degrees. Some people may take “realistic” as medieval (like the collection of taxes). The feudal system worked differently at different times and places and some specialists in medieval history want to stop talking about feudalism.
Otherwise, it’s a matter of picking a century and a country to represent the medieval. But different countries had different cultures and governments and economies in the Middle Ages, so there is no uniform medieval anything. Add to this the problem that specialists in medieval history disagree about what counts as medieval, and we are likely to get lost.
One way to think about this may be to ask, “What technology is not present?” Most fantasy settings lack industrialization, coal and electricity power, telecommunications, mass-production factories, high-power firearms, and a tight relationship between the individual and the state (poor census, no numerical identifier for the individual). Also, the typical medieval state itself was run by dynastic principles and personal ties.
Maybe what we need to think about is “pre-industrial societies.” There is a book called Pre-Industrial Societies by P. Crone. I recommend it to fantasy world-builders (but not in the 2003 edition!).