I think maybe you misunderstood. Yes at it's core it's still over 100 games you can play for $10/month and it's a great deal.
But these games won't include any of the DLC - that will be extra. Even current games like Forza Horizon 3, people say that the DLC is better than the base game. And Microsoft is pulling some interesting human behavioral responses in this area, because your brain says during a purchase decision "It's okay, the game was free so I can spend $20 on the DLC". The DLC will still add value to the game sure, but a lot of people are more likely to buy the DLC now since they got the base game "for free". I'm sure they have tons of market research in this area in regards to GWG titles.
My fear, which is hopefully unfounded, is that we'll see more egregious abusers of micro-transactions (think Battlefront 2) but people will be totally cool with it since, again, the game itself was "free". Anyone complaining about it will probably be told "it's not like you have to play that game" or even "you didn't pay for the base game so stop being ungrateful". Kinda like how if there's a terrible show on Netflix, people just kind of shrug it off and will tell you to "just watch something else". On that note, people are calling this "Netflix for gaming" which is somewhat accurate, I just worry it will turn into "like Netflix for gaming, where the first season of your favorite shows are free and additional seasons cost even more money."