Close to zero companies would accept this, even if your performance met standards and you did it in such a way you didn't miss a single meeting. That's why I said if you are open about it they will fire [or not hire] you. It's a double standard.
There is only one used method of performance measurement: time spent. Every company who CLAIMS to be "data-driven" or "gamifies the system" are lying through their teeth. They're like every other company, they measure performance by hours spent.
I've seen many engineers easily hitting double the number of tickets closed as others. They don't work 20 hours a week. If they did, they would be fired within days.
This is why over-employment is "cheating". Employers don't actually care about your performance, they care about how much you're paying. If you're paying less to them, even if their end of the deal is sweet, they feel cheated. They, like most Americans, value perceived fairness over actual outcomes. They have no issue shooting themselves, or you, in the foot if this looks to be more fair.
Now I could go out and get a retail job for after my regular job.
2. I'm not aware of anyone who is the CEO of 4 companies; well, except Mr Musk, but don't you dare say for a second that no one is batting an eye at that. Most CEOs I know barely have enough time for one company; and obviously the performance of Musk's companies recently suggests he's in the same boat.
3. The original poster pretty clearly inferred that, in these situations, generally speaking these workers are not meeting performance expectations.
If you want to work at 4 companies and your 4 managers don't have a problem with it, then go for it. Real problem arises when one lie about it and does it stealthily. Lying shouldn't be allowed, neither for CEOs nor for worker bees.