I dont see why anyone would draw an equivalent between Windows RT and Windows 10S. W10S limits running executables to only the ones acquired from the Windows Store, be it UWP, WinRT, Win32, or whatever that is.
On the other hand, Windows RT, as the name implies, only runs WinRT executables, which happens to only be distributed in Windows Store. Store is not the main issue here, but WinRT, which was a totally new thing at the time, plus the rejection of the general population towards the metro UI.
As an example, I dont expect iTunes to ever come to WinRT, as it requires re-writing the program from scratch, but uploading existing Win32 program to Windows Store is a totally different thing and can be done in a couple of days, or less.
Regarding Windows RT, I believe it failed not because of apps, not because of the consumer market, not because of Microsoft, but simply because of Intel. Near the launch of Windows 8 and RT, Intel released Clover Trail Atom that matched ARM CPUs battery life and speed, but offers x86 apps as its key advantage. Almost all OEMs went with Atom as a result, since there was no advantage to build a device using ARM and Windows RT. As a result, there wasnt many Windows RT devices on the market, and people cannot buy something thats not available. The only option for ARM was Surface RT and Surface 2, and those werent exactly cheap.