MS has mostly abandoned that approach now. But during Windows 8 days? Yeah. There was a legitimate concern that MS will lock down Windows and try to funnel everything through Microsoft Store, establishing an Apple-style walled garden.
The concern was serious enough that Valve took a defensive posture and started investing into Linux support. Which, at first, largely failed - but eventually resulted in Steam Deck.
For sure, and I'm glad they backed off from it. I'm also glad they did it because of how it pushed Valve into making Steam OS so good. But Microsoft really did want to go down the same path, and I do not trust them not to try it again.
The Surface RT that I tried absolutely was, and everything else I'm seeing to make sure I'm not misremembering shows that Windows RT was still locked down. So you should expand on what you mean.
Windows S Mode shows that Microsoft still thinks this is a good idea, too.
You might be mixing up Windows RT and WinRT. The former was Windows 8 for ARM with the Store as the only software source; the latter was the new set of APIs.
The concern was serious enough that Valve took a defensive posture and started investing into Linux support. Which, at first, largely failed - but eventually resulted in Steam Deck.