Interesting, yet complex.
And note that in level 15, where you gain access to level 4 calls but no new calls, you gain the ability to replace a call for another, same at every level where you gain no new call. so it shifts the balance a little towards the higher level calls.

But I think your idea on that 6th level chart might be a better idea, I'll try to work that out. (it will also allow a better split of powers. and a more steady improvement, less jumpy.

"tactical calls" like feather fall and such? might be handy, but they are not something you can bring from a portal. unless you got some ideas?

Anyway, ideas for new calls to fill the new 6 levels will help.