I think you misunderstand the purpose of immersion. You still have to dissipate and radiate the heat. You can’t just do it with “any approach” because air, as a medium, cannot conduct as much heat. You will reach a maximum in air long before you reach a max in mineral oil. But it isn’t magic. The heat has to go somewhere. That is why liquid coolers have radiators and why air-cooled cases have vents to the outside.
Yes, a stainless steel tank has thousand times more surface to disipate the heat away than a bare CPU. Same with 1-kilo heatsinks, like, for example, Noctua NH-P1 which I am using for passive air cooling today.
Absolutely. It's all about heat exchange contact area, nothing more. Contact area can be increased by fins, or simply by mass. A cubic meter copper cube would still cool down a CPU adequately even without a single fin. Of course, fins are space-saving so everyone uses them.
