Activision as a whole is a great acquisition, no doubt about it, but the value should come from the talent, not necessary the IPs. Not many IPs can last for 30 years, but they need to take advantage of all their studios to make new, fun and innovative games.
Sadly, I don't think things work like that anymore. Franchises, brands, universes, are the order of the day. Not creative minds and new ideas.
Most of the games in the best sellers lists are sequels, practically all of them. People know what they like and they like what they know.
The IP is the deal, not the workers, buildings, etc.
If you put COD vs signing Miyamoto's (or another celebrated designer) latest idea and wanted to make money, COD would be the safest bet, even if the new idea was more innovative, more interesting and more fun.
With that in mind, I would think Microsoft are correct that any major developer and publisher team could with enough money make a top tier FPS that the people who played it absolutely love. What this deal is about is that the game would likely be something of a failure financially because people will go for the game called Battlefield, COD, etc.