With regards to the rebate or whatever between retailers and AMD, could this be a misunderstanding by the retailers? Because how that looks to me isn't necessarily AMD upping the MSRP, but rather them trying to make sure that at least some cards actually do sell at MSRP (and in this case the lowest price), and not marked up like always happens at launch of new graphics cards. They offered the rebate for the retailers because they know they would lose out on money by not marking up the cards (so they're trying to let customers get the lowest price, but also trying to keep the retailers happy by not totally screwing them and in fact somewhat rewarding them for actually selling at MSRP).
Coupled with AMD setting bundles (which normally would be a way for retailers to up revenue by adding other stuff to get people to buy generally high profit margin stuff, and obfuscate their price shenanigans; but with AMD setting official bundle options it limits what they'd be able to do there), and retailers aren't happy as it limits their options, so they try to paint AMD in bad light to try to stop this from becoming a normal thing.
There absolutely does exist proof of what is happening. A deal like this would have a paper trail, either in contract (pretty sure rebates require legal terms, and if I was a company I definitely would not agree to any price and/or sale stipulations I wasn't in control of without legal terms to keep from being screwed), or at minimum financial evidence (with some manner of communication about pricing setup). It really is as simple as the retailers providing this proof if they want it to be accepted. They don't have to post it publicly, but the way they're claiming, I'd be talking to regulatory bodies about the legality of it.
Right now, this seems more like retailers just weren't happy that AMD was doing things to limit their ability to markup cards. Which that's fair for them to complain about to AMD, but they're trying to act like AMD is screwing consumers over, when I think its feasible that they're actually trying to keep retailers from screwing customers with ridiculous markups.
I'm skeptical of undervolting based on my personal experience. I remember reading about 50-100mV undervolt on 290/Fury/Polaris for forever. I've never had much luck undervolting AMD GPUs. My latest 480 undervolt attempt I ended up undervolting by just 24mV which doesn't save me any power. When I went for 39mV, I got a video driver crash less than 24 hours later. I think undervolting reports are like bad reviews, you tend to see extreme results on the net and think they're the norm when they're not. I think Balanced Profile from AMD is best optimization you're going to get, anything else is a lottery.
I don't think its all that rare (I see quite a lot of people able to easily get noticeable improvements and not even seeing how far they can push), but I think you need to tune more than just the voltage though to be able to get the full benefit (and possibly stability). Which I think the only way to undervolt 290 and Fury was with BIOS tweaking or special 3rd party tools, was it MSI Afterburner that was popular for that? Which the BIOS modding seemed to work the best, but that was also on AIB versions that tended to have more robust power delivery setup. Wattman didn't show up until Polaris, and in my experience you need to do more than just go and throw some manual voltage settings. It also seems to be buggy still (hence you need to tweak multiple parameters, and not always in the way you think, seems most people push the power limit up all the way for instance; from what I recall on Polaris you could generally change just the power limit down by about 20% and see a minimal performance drop but decent improvement in power use too without messing with other manual adjustments, which means you will lose a bit of performance).