The article is not very well written, but the argument is as follows:
1-Their games are very expensive to make. 1.5M€ for Furi is a lot. Haven’t played Haven, but what I’ve seen of it makes me think 3M€ is equally expensive.
2-They get very good first party deals that make such budgets less risky.
3-Without those deals their business model might not be sustainable.
That said, of course having a game in Game Pass affects sales. Not everybody who gets the game would have bought it, but subscribers that would have bought the game will not (it is pretty obvious). And since Game Pass subscription is very widespread (much more now than PS+ was with Furi), the extra word of mouth does not compensate. However, as things stand, for many bigger indies getting a game in Game Pass will net more money (significantly more) than any lost sales. That’s why getting there is important.
Now, having said this, I do not agree with their calculus, specially for porting full games. I doubt their porting costs (to any console platform) from a game already set up to be released in other consoles and built in a third party engine (Unity in this case) would be higher than an extra 50k€ or so if done internally (with a team of 12, quite feasible). And that’s a very generous estimate (half that would be more realistic, specially for a team that already has gone through the process). Even third party porting can reasonably be found for that price or less. For games with their budgets and expected sales, it’s just a rounding error (1-2% of total costs, and you are going to get more than 2% of sales per platform).
For the Furi DLC it might make sense not to port, if you ignore the PR issues (which I think is unwise for a studio with those sales numbers/cash flow, as the “outcry” seems to show). The costs are similar than porting a full game, specially with the underlying platform changes, but the overall DLC budget and the number of potential sales are likely way lower (say porting it’s now 15% of the DLC budget per main platform and you are not getting those 15% of sales on Xbox given current and former player counts).