1266 Mhz @ 890mV? Back when the 480 was released some guys couldn't even do 1300Mhz at 1200mv, those who could to get into 1400Mhz territory would usually need 1250+mV, of course there were some "alien" cards among the best aib models that could do 1400Mhz @ 1150mV, like some "special" XFX GTR s or some "special" Sapphire Nitro+. With this revision of polaris it is much more common to get such clocks at much lower volts, that msi rx580 in the video did 1400Mhz at 1050mV. These are not straight rebrands, the arquitecture is the same, but the manufacturing process is better, more refined.
I see this like the 3.2GHz Phenom II x4 955 BE vs the 3.7GHz Phenom II x4 980 BE, essentially the same arquitecture, but the latter had much higher clocks than the former at the same tdp. In hwbot the average oc for the 955 on water is 4138MHz, while the average oc on air for the 980 is 4270MHz. Despite being the same arquitecture, would you say that the 980 is a rebranded 955? Sure you can get a 955 working at stock 980 clocks, but when you push the clocks on both, the 980 will easily beat the 955 on average.
I'm not saying that what AMD did is 100% correct, this should have been called rx 485/ rx480 xtx/ rx480XT PE or something similar, not rx580, but these are not straight rebrands, this is how i see it.