But doesn't the removal of tier requirements significantly alter characters development as they level up? And you could keep the level requirements in your game, but its not really presented as an option--its presented as "this is how feats work now".
No more, honestly, than the addition of new feats to the game with any
new supplement.
I don't think existing feats are being changed in any way. I think new feats from here on out (or at least within Essentials) will be mainly designed without feat tiers.
That doesn't mean we'll see an Epic level feat available at Heroic levels. Instead, we'll see a version of it appropriate for Heroic level power which then slowly evolves into the Epic version at Paragon and then Epic levels.