meaning - What does "and are they ever " mean?

"And are they ever" means that they are to a very high degree. It is emphasising or intensifying the previous statement.

It is similar to saying that the over-represented paths are really really over represented and the under-represented paths are really really under-represented.

A simpler example would be:

Given the pitch conditions, the players should be covered in mud. And are they ever!

So the players are caked in mud up to their eyeballs.