I don't know what benchmarks you were looking at but RX 480 has similar or better performance to a single GTX 1080 according to what I've read.
You should read a little bit more:
Are two RX 480s faster than a single GTX 1080?
I love a good PR stunt or outlandish claim as much as the next guy. You know the type—where a company decides that the best way to tell people about a new product is to
slaughter a few goats and serve fake entrails up to guests or to declare that a certain developer is
going to make you his bitch. Imagine my delight, then, when AMD's Raja Koduri took to the stage during the unveiling of the RX 480 to say that, with two of them in Crossfire, they were faster than Nvidia's GTX 1080
and would cost far less. Everyone was intrigued.
Here's the thing about making bold claims involving competitor products, though: you'd better be damn sure those claims stand up under scrutiny. Sooner or later, someone will actually test it.
With the RX 480 in shops and the initial batch of press reviews near universally declaring it an excellent graphics card for the budget-minded gamer (
something I agreed with too), it's time to put AMD's bold claims to the test. Are two AMD RX 480s faster than a GTX 1080?
In a word: no. In fact, they're not even faster than a GTX 1070 in many games. To be fair to AMD, though, the company only ever said that two RX 480s were faster than a GTX 1080 in one game, under specific settings. So let's start with that one.
According to a Reddit AMA with AMD's Robert Hallock, AMD ran version 1.12.19928 of the game
Ashes of the Singularity under DirectX 12 at 1080p and multi-GPU enabled with crazy settings, 8X MSAA enabled, and v-sync off during its benchmark. Hallock also detailed the system specs, which included an Intel i7 5930K, 32GB of 2400Mhz DDR4 memory, and Windows 10 64-bit.
The result? According to AMD,
Ashes of the Singularity ran at 62.5FPS on the AMD cards and 58.7FPS on the GTX 1080.
While I can't replicate the exact same setup as AMD during its testing—I have a newer version of the RX 480 driver, for instance—I can get pretty close. The
Ars UK test system just so happens to be based on a 5930K processor with 32GB of DDR4 memory. I even have access to the same Nvidia beta driver. With that in mind, I ran the benchmarks on the GTX 1080 several times using both the old driver and the new driver, the latter to better represent the experience consumers have with the Nvidia card right now.
The result on the Ars UK rig? 55.2FPS to the dual RX 480s and 57.2 to the GTX 1080. So it's close—very close. But no matter how much I tried, I couldn't get the dual RX 480 setup close to the 62.5FPS figure that AMD quoted during its stage presentation. Weirdly with the newer Nvidia driver, its score actually
goes down, this time to 54.9FPS. It effectively matches the frame rate of the RX 480.
Either way, while buying two RX 480s and running them together in a very specific setup might get you close to GTX 1080 performance, they're aren't
faster.
How does dual RX 480s fare in other tests?
Widening out the dual RX 480 tests to include Crossfire in other games and benchmarks throws up some interesting results. Again, to be clear, AMD never claimed that two RX 480s would be faster than a GTX 1080 in anything other than
Ashes of the Singularity, but it is interesting to see Crossfire performance nonetheless. In 3DMark, for instance, the dual 480s are five percent slower than a single GTX 1080, the gap shrinking slightly to just over two percent at 4K. In
Metro Last Light, the RX 480s are 17 percent slower than a GTX 1080 at 1080p, with the gap shrinking to around five percent at 4K.
Yeah I have missed that I admit. It's not as fast as RX480 so I guess my prediction was right that NVIDIA wanted to match the performance RX480 with its 1060 to reach for mid range market of video cards. I would like to see the final pricing for the card. The range put on the web page you linked is over 50$ and still more than RX480.
More stuff then better. 
