Sorry, I disagree with your assessment.
Suppose there was no Gamepass, and Starfield released on Xbox/PC, and sold 20 million copies. That'd have been a success. Now in a post-GP world, they need to make the same or more money. Otherwise, in terms of lost opportunity cost, it'd be a failure. That money could either come from
new subscribers or
game sales revenue.
And also, although I don't agree with or believe Phil when he says it,
Gamepass increases game sales according to him. So more sales of Starfield should be expected at the bare minimum.
This is a vanity metric at the end of the day. User engagement or total number of players for a game will always be a vanity metric.