Like, I'll give you the laziest counterpoint in the world: you say that if someone makes a company and hires people and the value of the company goes up, the owner took that value from the workers. What if the value of the company goes down? What if the owner loses money? Did the workers steal that value? Did somebody steal that value? Or is your "basic numeracy" basically nonsense?
So, in this scenario, why has the "value" gone down? Is it as a
result of the employee's work, or is it independent, entirely unconnected (a result of external market factors maybe)?
If the former, then how exactly has that happened? Is it because they're a member of staff who isn't directly responsible for production, like an administrator, HR, or sanitation? If so, the employer has made a decision that their presence assists the functioning of the company long-term. The employer has made that cost-benefit decision.
Or is it because the employee's work is of such little value that they don't cover their own wage? How often does that happen? It's a hell of a lot less common than the other way around... and even when it does happen, the employer is the one who has fucked up recruitment. They still made that decision.
And if the devaluation is entirely unconnected, then you don't have a valid point whatsoever. The employee still creates value; the money made from that increased value is still primarily taken by other people. If the employee weren't there, then the value would be
lower still, and the discrepancy between the two figures is a
positive contribution on the part of the employee.
You've criticised someone else for boiling economics down to "basics", but this is surface-level misunderstanding of economics right here.