See this is a realistic perspective that I can completely disagree with but respect.
Like I said, I disagree with everything here, but I'll highlight just my biggest problems with it.
1). Powering GP with day 1 third party releases. This will just be much more expensive and make profits harder to come by, because the more subscribers you get, the more the publishers of these titles will want. Making the mistake of relying too heavily on third party content was what made the road to profitability for Netflix almost impossible until they changed course. Some of the numbers that get thrown around regarding money hats make me think you could quickly reach a point where these third party additions would be costing more than just developing games from scratch. I think MS is on the right track here, where the backbone of the service as far as day one releases will be built on their own content and additional day one content from third-parties will happen when the numbers work for both sides. It helps MS maintain an element of control that they would lose in the reverse scenario (third party publishers would realize that MS really needed their content in an extreme way in your scenario and would leverage that, which is just what was happening to Netflix).
2). First party titles being on GP will alter or limit the ambitions of a game. This I don't see at all, and several developers have voiced just the opposite opinion. If GP grows to a point where all the development costs for MS studios are just there with no sales pressure (all the sales on Xbox and PC would be pure profit/gravy), with the caveat being that needing to keep GP subscribers happy and on the hook is the primary pressure, I can see that being very liberating for both the devs and MS as a publisher. Todd Howard has even talked about how they loved the idea of GP even before they were part of MS, and how this type of arrangement can democratize content more and open the door for projects that just weren't happening otherwise. It's hard to think that the industry could get any more risk adverse than it currently is anyway. There will always be measures for success, GP won't remove that. If a game gets no sales on Xbox/PC and no engagement on GP, a sequel would be unlikely, etc. Or if a particular studio had a string of titles like that, something would be done there just as it would be in the traditional model.
3). I'm playing GoTG now, I've played Batman, I've played Superman in the past, I'll probably play Wonder Woman. I'm not sure what you are saying with this one. Spiderman is great and it's not on Xbox, that's the way the ball bounces, XGS will have a ton of great games that won't be on PS. That's the way it goes.