The problem again, however, is that spells/feats/options from multiple splatbooks are being used to prove a feat is broken.
They don't. Not every book put out by WotC can be tested against every option in every other book. It's simply not possible.
As I see it, if a feat works well with all the options presented in the core books, and in the book that introduces that feat, then it's balanced. The fact that it may break when combined with elements from other non-core books simply means that those specific combinations need to be nerfed or eliminated.
Or, to put it another way, no amount of work by WotC can eliminate the need for DM adjudication.