One last thought on this:
ZD is a permanent with a static effect. The best proof I can find that the functionality of ZD today is not a power level errata is the comprehensive rules. If ZD oracle text was exactly as it is on the card it would function the way it does today, not the way you would like it to.
The card text, "If Zodiac Dragon is put into your graveyard, you may return Zodiac Dragon to your hand" is a static ability that creates a replacement effect. From the comprehensive rules:
604.2. Static abilities create continuous effects, some of which are prevention effects or replacement
effects. These effects are active as long as the permanent with the ability remains on the battlefield
and has the ability, or as long as the object with the ability remains in the appropriate zone, as
described in rule 112.6. (emphasis added is mine)
112.6. Abilities of an instant or sorcery spell usually function only while that object is on the stack.
Abilities of all other objects usually function only while that object is on the battlefield. The
exceptions are as follows: 112.6b An ability that states which zones it functions in functions only from those zones.
Basically regardless of why the card was errata'd or what its original intended ability was, this is not a power level errata. This is simply how the rules of the game work. The card doesn't say it functions in any particular zone so the exception listed as 112.6b does not apply. This leaves us with the default of 604.2
You could still argue that you want a functional errata to restore original functionality - but you have yet to prove original functionality. But I don't think there is any argument that can made that it was changed because of power level.
Believe me, I would love to have fun abusing ZD if it were changed. I just don't think the basis for the change you want exists.