Your delusional if you think GPU and ASIC mining is comparable. ANYONE can buy a gpu and fire up a rig. yeah maybe the big boys could get thier GPUs from the source maybe 50% cheaper than the regular joe but at least everyone has a shot.
That's not true. In a GPU only world those with facilities near to negligible cost power can still push the difficulty so high that 'normal' people are to mine at a loss even using the same hardware. The GPU generation was also rather maintenance heavy and so centralisation again helps with that.
The difference is with GPU's there is no withholding of current-generation technology by the OEM's to reap the reward early. It may not differ much in terms of relative difficulty and centralization of hashing, but it would even the playing field in terms of efficiency and eliminate pre-order fuckups like mentioned above. Although I agree maintaining a GPU farm is a rather large P.I.T.A. compared to standalone ASIC miners...
Also things like depreciation of equipment (waste), wildly fluctuating equipment price (read: BMT), late shipments, etc would be considerably less of a concern.