Yup; boils down to how many people are willing to pay full price, and who those people are.
If nothing but people who were buying tons of games anyways continue to subscribe, it probably won't work out. If it's a healthy mix of people who were buying tons of games and people who weren't, it probably will will work out.
And hopefully people who weren't spending $120 a year previously but are now, are also playing more games. That's the other thing about stuff like GamePass, it's a great value, it's not some "Math Trick" to try to profit (like something like MoviePass was), it legitimately is a nice way for any gamer casual / hardcore or not to play some games.
Perfectly explained, and I'm glad you brought up MoviePass which some people believe this is an equivalent of (it's not)...
Just as a comparison, I bet these same people think that Disney putting Avengers Endgame on Disney+ has lowered the total amount of post-theatrical release revenue that the movie has brought it...Ignoring the millions that signed up for the service as soon as they heard it would be available day one.