Phil Spencer is right about one thing: Games as a service are where the big and constant profits are right now. In terms of business it makes sense to concentrate on those experiences. But he's missing two things, I think:
1. Competition. The type of game he's talking about are rarely exclusive to one platform holder. If he wants to attract the MP/GaaS crowd he needs to consider that most of these experiences can also be found on PS4, PC (aside from play anywhere) etc. And then you have to offer the customer some added value to get them to choose your platform over the others. Which leads to point 2.
2. Growing and cultivating a userbase big and engaged enough for GaaS experiences. These games function best when there's​ a huge pool of potential players where a committed userbase can crystalize. On F2P mobile and PC that's no big deal. On a more closed platform like consoles it certainly is. A huge part in making your platform attractive, I think, is what most here already said: diversifying and growing your games portfolio, especially with highly lauded and discussed SP experiences. Each and every one of those cater to different players, make the platform attractive and lead to a healthy system. And it's a healthy system with a huge and dynamic audience where you can turn those GaaS into big profit.
So I hope Phil isn't loosing sight of the bigger picture and narrowing his approach, which will only hurt MS in the long term, I think.