I don't really think Celebi is that bad for the metagame. I really miss a defensive oriented meta, despite never playing DP. I remember reading somewhere that Drumlax would be "the only legitimate form of offense" then, but it's interesting offense, and definitely better than the offense used in inferior teams that sometimes end up beating superior teams. Quoting you here, Borat: Good offense > Stalls > Bad offense > Good offense. And my limited experience tells me that with stalls I often lose to well built offensive teams used by players as good as me (or better).
Even then, I don't really think Celebi will be that great of a wall. In fact, I don't really think Drumlax will be the only offensive thing with a good chance to work. Marowak uses HPBug frequently even without Celebi, and Machamp usefulness isn't really lowered much if he had to use it as well. I can even see old standard SD, RS, EQ, Rest Wak of Turbodrum being useful as, with the correct para support, you can 2HKO that Celebi that comes as you SD, especially with Spikes; In addition, SlamST Wak would be a pretty good supporter as well I guess, for things like Drumlax. And you have these other drummers like Clefable, Zard and Quagsire. And things like Exeggutor, Gengar, Steelix etc would have a good chance of doing something productive if you want a offensive structure for the team I suppose.
Afterall, Celebi will usually be substituting one of the waters (probably the Celebi standard stall would be Celebi, Drumlax, Skarm, Raikou, T-tar/Rhydon/MissyD, water-type?) so the Exeggutor that faced Suicune could now be able to para Celebi, or the Machamp that saw Starmie could now be seeing Celebi, the Steelix that faced Cloyster is now able to paraslam / explode into Celebi etc. I think that even with Celebi, the meta will still turn into a more offesnive meta that it now may seem to be over time imo. And, if Celebi is seeding it's not baton passing (pursuiters).
Isn't Celebi a way to balance even more the gsc meta, Borat?