I do not have a complete and satisfying answer, but digging around revealed a couple of points of interest:
Johan Wower wrote De Polymathia tractatio: integri operis de studiis veterum in 1665.
He uses the word polymathia throughout the text, but I did not spot a word for a polymath.
The text is available in plain text, but the quality of the conversion is ...
Another option is to use aliquatenus. According to L&S (II) it can mean "To a certain degree" and "in some respects"
So as it seems to remark the restrictive flavor, I may say aliquatenus is indeed a good fit here, but maybe only aliquatenus-ly so.
Philistus,... ut multo inferior, ita aliquatenus lucidior (Philistus, as he was ...
An extremely common term in medieval Latin, often used in a philosophical context, is secundum quid, i.e. "with respect to something." Obviously, secundum is used as a preposition here.
It is usually contrasted with something that exists per se, i.e. "in itself," or simpliciter, i.e. "simply speaking."
You can find hundreds of ...
Without more context, it's difficult to know precisely what you need to say. However, quodam modo means "in a certain manner", which could correspond to "in a certain respect" depending on context. Similarly you could use quadam ratione.