I agree with most of what you said, but a nit: one perspective I've heard on the motivation for preferred stock is this:
Suppose I give you $10M to start a company in exchange for 10% of it. You then easily sell the company for $9M, keeping 90% * $9M = $8.1M for yourself and returning $900k to me. Preferred (non-participating, 1x) shares prevent this problem by making sure you can't just run away with the money: you have to actually use it to build the business.
People investing in the company in non-liquid ways (e.g., the founders or engineers, via opportunity costs) aren't in the same boat, because their opportunity cost can't be immediately liquidated.