Ah, okay - thank you.
Interestingly, the "player equality" stance is something I can appreciate. If flying was powerful enough to make a substantial difference in player efficiency, then there is an issue of inequality... But the meta-achievement solves that! If you want the efficiency of flight, you go and do the achievements required!
Where I can potentially sympathise, is the consideration of alts or players coming in late. But even then, you can make the meta-achievement shift to the new zones and reward players for roughly the same amount of work. So, for example, the Thal'dranath achievement that rewards flight includes 50 world quests on Thal'dranath itself, completion of its heroic dungeons (assuming it has any) and you can use its reputations to substitute for the launch ones.
You know, that kind of thing.