dalauder :
There's more money in the midrange market. For every person that buys a GTX 1080, there's ten or more that buy an RX 480. For every GTX 1080 Ti, there's a hundred RX 480's sold.
And there certainly is competition between the GTX 1060 and the RX 480, especially as more DX12 titles roll out.
UPDATE: I tried to verify my claims above and I can't. If you have a good source for sales figures, I'd be pretty interested. My thinking was sales of a Camry vs. Corvette vs. Lambo. This chart tends to indicate that it's more like 4:1 than 10:1 like I claimed: http://images.anandtech.com/doci/10613/segments.png
You had the basic concept right, the majority of GPU sales is mid-range to low end. There are a lot fewer people willing to pay $700 for a GPU than there are in the $80-$250 range. This is partially why they released the 480 first. and it worked, they got a fair bump in market share.
As for the competition, this is the current breakdown(price/performance)
RX 550
1050 > 460
470 > 1050ti
570 > 1060 3gb
580 > 1060 6gb
1070
1080
1080ti/Titan Xp
AMD is winning 4/5ths of the mid range and low end, Vega will hopefully change things in the high end as nVidia has been unopposed there for far too long.
As for the stock....I'm looking into buying some, but going to wait for it to bottom out first. I think this drop is more about stock holders selling off the make their profit, price drops and they will buy back in for Vega. buy low, sell high. The suckers are the ones that bought high and watched their stocks drop and panicked and sold off at a loss. With Vega, it's looking to be a end-of-Q2 launch, so we wont really know until the end of Q3 how it's doing...assuming there will be plentiful stock.