As a career programmer, I worked for several companies. Each time I took a job, I negotiated what I thought was a fair salary for my wages. Some companies also gave me stock options and one gave me founder's stock. When a company had a good year, they often gave generous bonuses.
Only when I took great personal risk, did I expect to share the rewards that come with a successful company. I was always grateful when I got more than I agreed to work for, but I never felt entitled to it.
A janitor working for a 10x company should not feel entitled to 10x of the salary as another janitor working down the street for another company that is struggling.
But hiring people who are compensated fairly does not make someone a billionaire. If you generate $300,000 of value per year and I pay you $200,000, then I'm only making $100,000 profit off your work. I could hire more employees, but value does not scale linearly indefinitely. Doubling my number of employees does not guarantee I double my profits.
No, if I want to become a billionaire within my lifetime, I need an asset that generates far more money than it costs to buy and maintain it. In other words, I need employees who will generate millions for every thousand I pay them.
Now you might well argue that I'm taking a risk. How do I know if an asset or an employee or a team of employees is undervalued? Not every bet is going to pay dividends. However, while this is true, I don't think this makes it ethical. If I'm a venture capitalist looking to make it rich (or richer), the fact that I'm taking a risk doesn't change the fact that ultimately I'm looking for people who I can pay far less than they're worth.
Even within successful companies, it is a challenging task to figure out just how much value each employee produces. Some positions are required, but do not produce revenue. Sometimes whole departments are a sunk cost.
It is up to each employee at review time, to argue that the value they produce is far greater than their salary; in order to negotiate a raise. No one is automatically entitled to anything extra, just because the company had a good year.
If I charge a client $50k for some software and they made $1 million profit from it, good for them? As long as they pay our mutually agreed upon rate on time and there was no hostile negotiation, why should I feel suddenly entitled to more money if that wasn't in our contract? How do I know how much of the value is from my work and not their marketing or idea?
What you're saying seems as crazy as me saying that someone who bought my software for $99 and used it on a multi-million dollar project is being unethical unless they give me more money. How on Earth does that make sense? Should I be forced to switch to a royalty model? What if I make more selling copies at a flat rate, what if I don't want to have to investigate the finances of thousands of customers and have to deal with that whole trouble?
For me it's the same thing regardless of whether I'm selling my labour or a product. I can choose whether to accept a flat hourly rate, equity, or a mix of both, and usually the better deal is the hourly rate.
If I find a way to hire a software engineer for market rates (say, $200k/year in the US) and get $2M revenue from their work, good? They can ask for a raise or a bonus, we can renegotiate, they can leave if they're unhappy, but I'm not obligated to give them more money than was in our agreement anymore than they're obligated to give me their salary back in the project fails.