The nymphs are possibly inspired from Dante manuscripts

[Rafal]

Weren't (most) MSs in the middle ages simple copies of existing works, instead of a mish-mash of tens of different sources?

I would somehow agree.

Medieval books often feel very repetitive. For example each Book of Hours is unique but at the same time they boringly copy the same motifs all the time.

And Voynich Manuscript indeed seems to be a true mish-mash of many, very different sources. A kind of medieval collage. It's quite unique in that aspect.