A lot of gaming sites asked developers whose games were on GamePass what they thought of it, and the answer was predictable. Like, nobody is going to ill talk the provider of the service their game is on.

Other developers didn't speak ill of it because of the fear of burning bridges, I suppose.

The Game Bakers (Furi, Haven) talked about their difficult relationship with GP on Vice (LINK).

“Game Pass is such a fantastic platform for players,” said Leprince, “so there are possibly more Xbox players than ever interested in indie games. Unfortunately, without Game Pass, it is also very hard for many indie games to be visible on Xbox.”

Basically, the problem with a subscription service such as GP is that it cannibalizes other games' sales outside the service itself. And since you are not guaranteed to land on GP, developing a game Xbox may be more of a gamble than it is on other platforms. I fear this may become the norm as more subscription services are rolled out and start encroaching the market.

There's also the problem with founding. Furi sold 78% of its copies through PS+, yet only one third of its budget was paid by Sony for the deal. Developers have to decide whether they need less money immediately, or potentially more money down the line; but for indie developers, sometimes there is no choice: they either accept the deal, or shut down because they don't have the founding to complete their next game.

I really like the Vice article I linked because it's one of the very few who tried to analyze the situation impartially, with data backing it up. Most of the other industry journalists at the time were like "GP is the future! Gamers spend less and everyone gains more money!!1!", parroting Spencer's bullshit.