It is crumbling clearly, because idea of lock-in was to prevent using non Windows systems to run games. And it's not working out due to technology doing wonders translating lock-in graphics APIs into open ones with good performance.

Using APIs for lock-in is an old anti-competitive trick, so it's fun to see it failing for gaming.

Windows game developers couldn't care less, Valve takes over all the porting costs, while Windows focused game studios get all the money, with increased sales, without caring one second about GNU/Linux.

A Phyrric victory if there was one.

Lock-in was MS's game here, not game developers'. MS used game developers' reliance on DirectX to make getting games outside of MS systems harder / more costly due to the need for extra porting. Does it make it more clear? So what Valve did is a smart knight move that breaks MS lock-in.

As long as it emulates Windows and DirectX, they have achieved nothing, specially when SteamDeck clones running Windows 11 take over, as expected during 2024.

Now had they managed to convince said studios to write native GNU/Linux games, or to port their Android/NDK games into GNU/Linux, I would have agreed Valve managed something.

No point to repeat the same thing. Your "achieved nothing" is an empty argument.