I swear, people throw around "OP" so much on this site that it has lost all reasonable meaning. What does it really mean anymore?
OP is what it is. It's your opinion (or a consensus of opinions) of how a rule or system within a game detracts from other parts of the design. Of course there are varying degrees of what everyone considers balanced, but no-fuel creative flight for killing a bat... what the hell, you might as well /gamemode 1 and be done with it. That's cool if you like god-mode early in a map (I often do), but you already have the option to cheat stuff in, go creative, or play on a server with that kind of ruleset. It's not taking anything away from you if a pack designer or server admin tries to create some semblance of a progression-oriented experience.
On that note, Advanced Genetics gives you the same creative flight for punching a bat with a spoon, running that through 5 or so machines (if you get the lucky gene) and injecting yourself with the result of the bat gene plus about 28 others. Even in this ... semi-unbalanced implementation (in relation to other forms of flight presented in the pack), you have to at least DO something.