Using your examples, Healing I is so incredibly boring I yawned while reading it. That has more to do with the terrible state of healing in D&D, but it's still there. Also, every cleric ever takes War I & II and never takes War III. They instead take Death III and cackle madly. You would definitely have to re-balance the domains (or whatever grouping you choose) to ensure that every path has viable options at each level.
The idea itself has merit, but needs to be tweaked to be playable. For example, while clerics can get away with having only 1 spell at level 1, because they're also fighters, Wizards can't. That is where the shadowcaster fails hardest (mysteries also blow for the most part, which only exacerbates the extremely limited uses they get).
What you could do, however, is grant a number of slots at each tier equal to your choices in that tier modified by the tier multiplier (x1 for spells, x2 for SLAs, x3 for su.), which can be used to cast any spell of the appropriate tier you know. Functionally, you get 1 slot per spell you know, 2 slots per SLA you know, and 3 slots per su. you know, which can be used to cast any spell of the relevant tier. Do that, and hand out enough spells known, and you'd be fine.