Yes, past 10th all you will get are feats, spell slots, and class features. I feel casters lose a lot more than the melee though since they lose access to knowing spells of 6th level and higher. The way I envisioned it is that melee classes usually have class features every few levels, so they would still be gaining them. On the other hand a wizard/sorcerer/cleric who normally prestige out due to lack of class features would still get the opportunity to try whatever build they wanted, just with a restriction on spells known. In the event someone took one of these caster classes to max level they would still gain their spell slots, just not spells known.
Maybe my wording was unclear, but for them to take that proposed feat they would have to be level 27 with 10 ranks of spellcraft (as the normal rank cap is level+3 if I remember correctly) since it normally requires 30 spellcraft.
The setting I intend to use was actually inspired by ToB as that is one of my favorite books, and I have encouraged the players to pick initiator classes. Though there are some who wish to be casters and I do not want to prevent them from that. I suppose I just don’t want the caster players to trivialize encounters with the spells once we are in the higher end of the level spectrum. Would it perhaps be better to just comb through the higher level spells and adjust them?