I hate Windows 10 more than most (look at my post history), but they're not fucking up Steam or any other general program and they're not going to.
What, specifically, is Windows 10 doing now that supports these claims? Steam (the client) is a buggy all on its own, and it has been since its inception. It's no longer worthy of the "Steaming piece of shit" nickname, but it's still pretty sloppy, ugly, and slow and if you ever have problems with the client not properly downloading/verifying game files, not properly syncing your library, crashing, or just not working, good fucking luck. Valve's "support" is 2 rounds of automatic responses from a robot and then silence.
Further, Tim Sweeney is an ass. Why should we listening to him? And why is he moaning about this shit now? Valve stopped crying about it years ago. They were afraid that Windows 8 would result in people using the MS store so they cried and whinged to anyone who would listen about MS is locking down the PC, how the Windows store will be the only store, etc. Oh, and Steam just so happened to have a half-baked plan to stop them - SteamOS with big picture mode! And Steam-branded PCs that make PC gaming as easy as console gaming, at triple the price!! And a half-baked controller was coming soon!!!
I don't know if Valve stopped crying about Windows because it's been years and no one left Steam to use the Windows Store, or if they are quietly giving up on the push for Steam OS after realizing how much work maintaining an OS is and how few games are going to use OpenGL or Vulkan, or if people stopped listening to their FUD after years of 8/8.1/10 with zero lockdown.