A bit confused by some Eidolon evolution stuff

[Yemeth]

Can anyone explain why burrowing is more expensive and available four levels later than flight? I'd always assumed that flight was considered the best form of movement, at least in general.

[Arbane the Terrible]

Burrowing goes through walls. Since one point of a dungeon crawl is that the GM gets to restrict when you can go anywhere, being able to bypass all that is a big deal.

Plus, fliers can be shot at. Very few attacks will go through the ground.

[Yemeth]

Huh. The ability doesn't say anything about burrowing through solid stone, I thought you had to have additional special something like Earth Glide to pull that off?

Not being able to be attacked makes sense though. It is a pretty decent defensive tactic now that I think about it. Makes for a nasty surprise attack as well.

[Arbane the Terrible]

Looks like you're right about not being able to burrow through solid rock - that's what I get for not checking the book.