I love how it's assumed, taken as axiom, instead of absurdity, that it's even possible for a company to own a individual's time and mind by contract.
None of this has anything to do with Zenimax owning his "mind" or "time." It's about Carmack using company resources to enable Oculus. This becomes even more concerning when you consider that Carmack was one of their most senior, if not THE most senior engineer at the company. He's compensated handsomely under the assumption that any great ideas he has will end up with the company. This is similar to executive compensation strategies and carries with it very similar assumptions. The situation is a little more than some ordinary employee exploring their hobby and getting lucky.
This is like a CEO getting hired, being awarded a multi-hundred million dollar contract, not doing a single thing for the company that hired him, advertising for a competitor, leaving once his contract is up and also convincing numerous other executives to leave with him at the same time. That's extremely unethical in my opinion.
How much all that is worth is debatable, but the court seems to think it was worth $500M.
zenimax didn't have a VR headset to sell, or plans to make one
Imagine if this story was about carmack getting access to a playstation 4, and helping improve it and doing a demo of Doom on PS4.
that...is what he is supposed to do!
Your allegory is ending a bit too soon and missing some nuance: Imagine if this story was about carmack getting access to a Playstation 5 prototype, and helping improve it and doing a demo of Doom on PS 5. He then leaves Zenimax to work for Sony - on the PS 5