Feats should not be needed for basic mechanical function. And for everything above t4, that's true.Let's reverse this. Tier 3 and up should require feats to function. Tier 4 and below shouldn't. You want more power? Build harder. That's fair.
"Fair" depends on how you measure it, and I do not think feat taxes are the way to go with upper tiers. The imbalance problem isn't about how hard it is to build something: as soon as one person knows how to build it and posts it online, everybody else knows too.
If one's goal is to make things "fair", it makes more sense to nerf the actual spells rather than nerf it through a secondary system such feats. If tier 1-3 classes are tier 1-3 only if you choose certain feats, they are still tier 1-3, and the root problem remains. It would be a net negative for everybody: the high-tier players because they are narrowed into a few builds, and the low-tier players because the imbalance has not meaningfully changed.