I think that power creep is in some way a given, just as a meta is inevitable (re, the inevitable meta, Extropia makes a good case for that here). The only way to prevent power creep would be to have the newer stuff be less powerful than the older stuff.
What I would object to is if power creep were a marketing strategy by FFG, but it seems to me that (ACD Phantom notwithstanding) they do their best to keep the game as balanced as they can. Of course, they're only human and with every new wave the complexity and amount of unforeseen combinations increases. Even if they were to employ mathwing wizards (like MajorJuggler and Vorpal Sword), at some point imbalances would creep in. The best they can do is to keep things fluid so that the true efficiency peaks are changing and in need of being found.