I'm an amateur econ at best, but everything you said is generally true. I usually consider the extremes then tween them. If market cap is $100, somebody selling $10 would flood the system with supply, reducing price. With a $100T market cap, selling $10 wouldn't make a dent.
At these scales, trading and price act more like pressure and temperature, rather than individual trades moving the market. A tire with already-high pressure will take a lot more air to raise the pressure than a tire with low pressure.
