Today there are many more games that run on Windows than on Linux, that is a fact.

Sure, nobody is disputing that. Another fact is that most games that run on Windows also run on Linux. I don't have hard figures (feel free to browse Proton DB for specific games), but it's extremely rare for me to try a game and for it to not work properly, unless it uses certain anti-cheat systems. If you largely stick to single-player games, most will just work w/o any tweaks.

On the contrary, having access to Xbox Live seems to me to be an advantage.

Sure, and that's exactly the kind of lock-in you seemed to be so against WRT Steam.

You can always claim that you can do everything on a steamdeck, it is not necessarily straight forward and within the reach of the newcomer.

If you stick to Steam, most games just work. In the vast majority of SP games, you press "play" and the game runs, and it works like a console.

If you want to play games outside of that console experience, then it works like a PC, with the main difference that you install stuff through the app store (like you would on a phone) instead of over the internet. So as long as you know how to access the desktop (hold the power button and select "desktop") and to use Heroic for GOG, Epic, and Prime games, you're done. You install Heroic, install your games, and you can click play right there. Games tend to work better launched from Steam, and Heroic can automatically add it to Steam for you.

Dev mode is absolutely not necessary and not advised. And the above complication (again, not hard at all) is only needed because GOG, EGS, and Prime refuse to offer their own clients for Steam Deck. They could totally make a fantastic UX on that platform with relatively little effort if they chose, but I'm guessing they don't because the market share isn't high enough.

I honestly prefer to use Heroic vs GOG/EGS/Prime on Windows because then I don't have to deal with those separate launchers. Try it out, it's pretty great!.

the number of software in the libraries

What software do you realistically want to use on a Steam Deck that you can't? Are you seriously going to use MS Office or Adobe products on your handheld? The handheld form factor is intended to be a gaming system, not a laptop replacement, and using it as a laptop replacement is far more down the line of "power user" than accessing desktop mode to install an alternative games launcher.

I've used a browser maybe a handful of times on my Steam Deck, because using a browser on a handheld is a pretty crappy experience despite Valve going out of their way to make that experience as good as possible (trackpad navigation of keyboard is about as good as I can expect it to be, but it still sucks). Yeah, I could connect a USB hub to it and plug in a monitor, keyboard, and mouse, but why would I do that if I'm already a PC gamer instead of just using my PC?

Since 2013, Steam has an overall market share of +75% on any digital distribution, in Europe this share exceeds 80%

That tells me people really like the platform, especially since Steam does very little to keep you on their platform. They have no exclusives aside from first party titles (and those are pretty limited), they have no requirement to use DRM (and many games use no DRM), and developers are free to sell Steam keys on their own w/o sharing any of that money w/ Valve. Valve literally only profits if people buy games on Steam. They even make it easy to install alternative launchers on their Steam Deck and play non-Steam games within the Steam interface, and you can literally never buy a single game through Steam and still get the benefits of the Steam Deck.

Yes, they have a massive marketshare, but it's not because they're locking anyone in to their platform. On the other hand, Microsoft's Xbox software only works on their OS, their store only works on their OS, and they try to get game devs to use DirectX which is also only supported on their OS (though Valve and the Linux community have done a good job making a compat layer for Linux).

So if you're against monopolies, you should be against Microsoft, not Valve.

buy directly from his home site and do not go through a platform.

Sure, and you're absolutely free to do that and still play those games on Steam and the Steam Deck. Try that w/ any other games platform:

• PlayStation/XBox - any purchase sends money to the console manufacturer because of licensing rights
• GOG/EGS - I've seen occasional keys available through Humble and other retailers, but not directly through the dev
• iOS/Android - until recently, you were stuck w/ their app stores, but recent lawsuits are changing things so now alternative stores are becoming available (at least on Google, not sure about Apple); still can't side-load directly from the dev on iOS, but that's always been a feature on Android (but not commonly used)

On Steam, you have two options:

• buy a key from the dev directly and add it to Steam
• install the game directly from the dev (pretty rare these days) and add it as a non-Steam game

I've done both, and both work quite well. GOG can do the second, but AFAIK the first really isn't a thing.