Saw this online and thought it recapped things short and sweet:
1. The deal means more money and more time for MW5. This means a better game. IT also had to be delayed in order to avoid Borderlands 3 and Gears of War 5 that is dropping right on top of MW5's original Sep 10 release date.
2. We get German, French, Russian localization, more marketing push, and hire more employees to polish the game
3. The recoup point to be successful for MW5 is 750.000 units instead of Steam's 1 million
4. If you don't like the EGS, you can get a complete refund and keep all of your preorder MWO content
5. The game will come out on Steam and GOG next year and will benefit from more patches and more mods from the dedicated modding community
6. This deal lessens the financial risks, gives more marketing, a better overall and polished game, higher chance of success and more Mechwarrior games, and finally you can get your money back and wait, and it'll still be on Steam and GOG later