Limiting Prepared Casters a Bit (Spirit Shaman Casting)

[Datalore]

I was fiddling a bit with some rules today. How would a casting system like this work, do you think?

LINK

The idea is to maintain some of the flexibility of the prepared caster over a Sorceror/Oracle but make that come at a more significant cost (significantly less spell choices in the moment; significantly less casts per day; etc) while addressing some of the issues with typical spell prep systems.

Would a Tier 1 caster using such a system drop a Tier or stay the same?

[Create Mr. Pitt]

It's practically unusable at early levels for 1/2 BAB caster like wizard. Practically no spells save cantrips for a long period of time is boring and will probably lead to death. Ban certain casters if you want (though I wouldn't) don't nerf them into oblivion.

[Datalore]

Same total spells prepped as a Spirit Shaman though (slightly more actually) - just less casts. Just curious if they would be tier 2 with something like this.