It's the difference between a smart TV and a dumb TV. They have different guts but the market is the same.
Major titles like Beat Saber or Half Life Alyx can be played on either standalone or tethered headsets. Facebook offers both under the Oculus brand and positions them together: https://www.oculus.com/compare/
Rift S is discontinued, their marketing materials notwitstanding. Half Life Alyx can only be played by a standalone headset if you let a computer run the all the graphics and game logic, similar to how an iPad can be used as a second monitor for Apple devices. It's really quite different from smart/dumb TV.
It's the same. The market is VR gaming. People who want to play VR games choose what headset to buy. Simple as that.
The TV/iPad comparison doesn't work. It's very common to have both a TV and an iPad, but I have yet to meet anyone who has both tethered and untethered VR headsets, and thinks of them as distinct.
The VR market is small and may differentiate in time, like how "mobile" has grown so it's common to have a phone and tablet and laptop. Bringing down the antitrust hammer today seems so premature.
Major titles like Beat Saber or Half Life Alyx can be played on either standalone or tethered headsets. Facebook offers both under the Oculus brand and positions them together: https://www.oculus.com/compare/