If every single person paid to work on AWS leaves the company overnight, what happens to the value of AWS? Sure, Amazon could eventually hire enough people to replace those who left and maybe even keep AWS running and develop new features but it would be a catrastrophic loss of value and take a long time (and a huge investment) to recover.
You don't create value by having capital either. Labor converts capital into value. Labor can also transform capital (e.g. produce code which can then be used to provide a service for money). Plenty of people have "ideas" but ideas are worthless in a vacuum. If you pay someone to turn your ideas into capital you can use to generate value with cheap labor, your idea didn't become valuable by itself, you literally paid for labor to refine your capital to become better at generating value - you may legally own that refined capital the same way you owned the initial capital but the transformation had nothing to do with you other than your means to pay someone to perform it for you. Your money didn't create value, it merely facilitated the transformation of your capital and the creation of value. Your individual ownership of that capital is entirely unnecessary in this.
The tech, knowledge, software, etc of a company is a multiplier for the value labor can produce. It still requires labor to produce that value. It also requires labor to maintain that multiplier, much like literal machines require maintenance. The industrial era analogy still holds true (and arguably even more so given how specialized individual jobs can become).
The total cost of employment is generally not an order of magnitude more than salaries. Wages are the biggest cost factor in most companies, especially in companies built on knowledge work (e.g. software). The biggest employee expenses (though usually defined in terms of easily obtainable bonuses and often with severance packages other employees don't have access to) are CEO and other CxO-level positions. This isn't because of a natural value of these positions to the company, this is almost entirely the result of years of advocacy to investors and boards promoting the idea that these positions should be paid several orders of magnitude more than everyone else with very little factual evidence to support that idea - it's pure ideology and it's fairly recent.
The overheads are irrelevant for the general point, too. Corporations need to make a profit to function. Corporations don't need to siphon that profit almost exclusively into CxO-level benefits and shareholder dividends. You're right to argue that if a company makes $1,000,000 per $100,000 employee, that doesn't mean it makes $900,000 in profit per employee. But even if the operating costs are so high it only makes $100,000 profit per employee - that's still money left on the table (which the individual employee has no leverage to demand a fair share of).