A few thoughts after reading...

[hit_fido]

Your missing the forst for the trees. The actual numbers on the tier gates are irrelevant; the underlying mechanic is the key. The underlying mechanic you propose is fundamentally more restrictive (and forces way more wasted AP) than the underlying mechanic on live

Removing AP gating releases a restriction. Relying on enhancement pre-requisites to gate other enhancements is in place on Live right now so that's just incorrect.

OR you allow high power enhancements to be taken at low levels, which is unworkably unbalancing. Consider 0/10/30/50/70 as the AP gates, or any other variation you please.

This is the fundamental mechanic in action. Higher power enhancements should not be available until higher levels. Your proposal does nothing to ensure this. Explain in detail how you propose to force the higher power enhancements to later levels.

I'm fine taking specific scenarios and looking at them case by case because that may prove enlightening and may be good fodder for Turbine. Favored Damage I can be taken on live right now at ranger level 1. Favored Damage II at ranger level 5, and III at ranger level 9. So your system is actually more restrictive than Live, and in my opinion more restrictive than necessary in this case. It is not overpowering on Live that a ranger level 5 can take +2 Damage against favored enemies; if we did nothing more than dump AP gating, then a ranger level 4 could take +3 damage against favored enemies - hardly a significant difference. So, this is not a scenario where we need to worry about overbalancing power at lower levels, but it is a scenario where your proposal deviates from Live in the direction of more restriction. Note that it doesn't matter if you decouple the enhancements; your proposal still limits any favored damage increases to character level 8, and my proposal still limits it to ranger level 4.

My position is still that eliminating AP gating is a net good regardless of whether we tweak enhancement chains or not. Now what I'd like to see is an actual scenario based on removing AP gating and changing nothing else in what we've seen so far that is demonstrably game balance breaking because of the lack of AP gating or more restrictive because of the lack of AP gating. I haven't yet, but do not claim it's impossible - it seems to me that is the demonstration that is needed to refute my position that removing AP gating altogether is an absolute net gain.