It's really not. The browser does have some new innovations... But it isn't something new from the ground up.
EdgeHTML is a fork of Trident. They dropped legacy code, and fixed a ton of things... But still a fork. In fact, EdgeHTML was available as an experimental feature in IE11.
Chakra is a fork of the JavaScript engine that was running in IE.
Edge is nowhere near a brand new browser. But it does look like they're on the way to get IE right under the new name. (Though security still needs some more work, apparently.)
https://www.microsoft.com/en-us/research/publication/the-mul...
Here's recent work on securing networked apps:
https://www.usenix.org/system/files/conference/osdi14/osdi14...
They're capable of making most of a browser immune to attacks likely to hit it. They can also make a strong system for containment. These simply weren't present in Edge to degree MS Research had designed. There's something blocking the transfer of those quite-practical tech that MS Research has been building.
Secondly, it is interesting to see that all (except one) security teams, that won the contest, were Chinese teams. I am surprised at the absence of US/Russian/EU hackers. Perhaps they are selling their exploits at much larger premium in black market, to NSA et all.