Yes, thats basically it. Each pixel of an OLED is self-emissive and can turn on/off on an individual basis. Vs a LCD tv that has a backlight (dimming zones) lighting up the LCD panel.
There is definitely some panel lottery involved, no manufacturer is perfect and I guess it comes down to which negative would bother you the least. I've read the dirty screen effect is worse in the larger panels like the 70+ inch ones. I'd suggest if people have doubts to buy from a store with a good return policy. Buying through costco with their branded credit card gets you a 5 year warranty, tradeoff is a smaller selection of tvs. LG has a 5 year manufacturer warranty on the LG G1 (not sure about the c1). I don't know much about samsung warranty.
Or for people with the money, they can buy a pre-calibrated tv
https://valueelectronics.com/product/q-c-and-calibration/ I am only recommending this site because I know about their procedure. They'll take tv out, run it through a battery of tests and calibrate it, but if it doesn't live up to their standards, they will not ship it out and keep opening boxes until they find a good one for you. On a side note this is the only company that Panasonic allowed to sell their tvs in the US (I heard it took him several years to convince them).