The Windows phone entered the market while the market was stable, and users had little reason to move away from what they were used to and comfortable with. These days users are getting more uncomfortable, hence why Linux is on the rise. Same with the push for more liberal software (FOSS). I believe if a company can do it right, and offer a stable and comfortable alternative, they can manage to be much more successful than the Windows phone was 10 - 15 years ago.
Disclaimer: I haven't checked the statistics, but I remain optimistic, and continue making choices that align with my principles.
You seem to look at it quite pessimistically imho, but I'll try and counter ;-)
We're not talking about a vastly different ecosystem. Probably Android-derived (which is open-source), very likely Linux derived. So compatibility is not going to be a huge issue, hence developing not hard. Developers will usually follow where user demand goes, not the other way around.
Most of the big apps today have a smaller equivalent, check AlternativeTo.net.
Generally true, but we're talking a growth of millions of users a year. Millions of people is no small number. 5% of the US' traffic are from Linux desktops, according to StatCounter (here's an article with many links).
You're correct wrt. gaming, as 2.89% of 157 million active monthly users is about 4.55 million, which is not a small number either. If you look at Linux desktop users in the US however, we're talking over 5% of 347 million, which is 17.35 million users in the US alone, which is also not a small number. It's more than the population of Greece and Bulgaria combined.
Do you have numbers? I can't find any official numbers of active users on the Steam Deck, but there are estimations of 3+ million devices sold. I feel like I keep seeing posts of people who move over to Bazzite and similar distros these days for the sake of playing games, but nevertheless, both of these factors weigh in, and are steadily increasing the adaptation of Linux systems.
This is denying the antecedent. The amount of games, and money in games, without KLAC is plenty substantial to make a difference in the approach of both developers and DRMs, further increasing ease of adaptation by users. Do not undermine nor underestimate the potential of marginalities.