That's exactly why they are a better choice, like the imaginary bridges on current Euro banknotes.
The selection of people is also quite poor but that's because people are a poor choice: Most notable historical people are very linked to specific countries, often against other countries so picking neutral ones is hard. They also clearly decided to have an equal number of men and women, which makes it even harder. Obviously there aren't enough different banknotes to represent every country, either.
Exactly.
Faces are a terrible idea for a common currency shared by 21 countries.
You have to pick one writer, good that the English left for good so Shakespeare's out, but how do the French feel about Cervantes vs. Victor Hugo?
The Poles complaining that they didn't get enough recognition because Marie Curie's maiden name isn't given enough prominence should tell you all there is to know about this being a good idea.
They could have done the same thing they did with the coins and make every country put their own faces in there.