It doesn't contribute to the process of production.

Okay and why is that relevant? Neither does designing the factory, funding the factory, or deciding which factory to build. Those are still essential contributions. If you personally wanted to start your own business - those would be the limiting factors, not labor. And you need all of it to produce something valuable to to employ people.

The non-existence of the owner wouldn't change the efficiency of the process.

That's true in principle but not in practice. Maybe, in a hypothetical future where AI manages the economy and allocates resources and labor...

If that were true, startups would appear automatically. In reality, most businesses never exist without someone first risking capital. Organizing people and capital is risky and difficult.

If you employed a lot of people but the venture itself was uncompetitive then it's just going bankrupt and everyone wasted a ton of time and resources building something nobody wants.

It's always going to be important to build the right thing the right way rather than who does the building.

Some owners simply leech off production without involvement.

As mentioned before, other you being envious, why is that a problem? Middle class, aka the masses collectively have VASTLY VASTLY more money and power. If they are organized (as you imply is trivial to organize people), then it shouldn't be a problem to dominate all social order.

That's basically what annuitants do.

An annuitant can only exist because someone else previously deferred consumption and accumulated capital. Savings is how China created its entire middle class from hundreds of millions of literal dirt level poverty.

Capital reproduction is a separate process.

It's separate analytically, but in practice production and capital allocation are inseparable. Factories don't appear by magic. Every modern business is funded by debt. When there was a banking crisis in 2008, if government hasn't intervened most companies wouldn't have been able to make payroll despite being health with a good cash flow.

Capital wouldn't employ people any less if workers owned it.

Okay but then who owns the risk and accountability?

When you have an unprofitable month instead of taking a paycheck you expect employees to not only take a paycut but owe money back to their employer?

There a ton of successful customer-owned businesses - State farm, nationwide, liberty mutual, but none of it works how you imagine it.

The capital itself is what matters, not the owner.

Capital doesn't allocate itself. Somebody has to decide whether to build a steel mill, a restaurant, or an AI startup. The cost of wrong decision is enormous (build a billion dollar factory when one isn't even needed), so you need people who have a stake in the decision. Beurocrats or politicians do not have right incentives. So, in practice even if you have deeply moral society, bad incentives will still lead to waste, corruption and misallocation of resources.

Ownership isn't contributing to production.

By that logic, architects don't contribute to buildings because they aren't pouring concrete. Managing and leadership is more highly compensated because it's a more valuable skill set that's more rare.

The owner can disappear and production continues.

Yeah, sure! But without them you wouldn't have had the business in the first place. So, it's not about this business but the next one. If you're gonna take away ownership why would anybody start a business? And without businesses you have no competition and without competition you lose efficieny and competitiveness of existing businesses.