You replaced your boss with a customer. No real change there; You're still at the mercy of someone. I'd say you're a dumbass for not realizing this, but I'll decline to as we're supposed to keep a higher standard here on HN.
A boss can fire you even if you are bringing in a profit. All it takes is 1 bad day, or a mistaken belief that someone from India can do the same job for half the price.
If you are the owner, it doesn't matter if one or two customers are hard to deal with. All you do is stop selling to them, and you will most likely still be in business.
A board can fire you and your whole team even if you're profitable. All it takes is 1 bad day, or a mistaken belief that outsourcing to a team in India can solve the same problem for half the price.
"Not worth more than being laid-off" would be hyperbolic, but I'd guess that your private company non-preferred shares are worth a lot less than you think they are. I have stories from real, "successful" companies that screwed over everyone not currently on staff on exit. It's not hard to do.
If shares of your company were undersold and you lose controlling interest in the process, that is your own fault. Founders usually have a different class of stock which has more voting rights per value.
This is like an employee accepting a $10/hour contract, and then complaining later that it was too low.
If you are the owner, it doesn't matter if one or two customers are hard to deal with. All you do is stop selling to them, and you will most likely still be in business.