no, you are not. but is is somewhat more complicated.

you want to end up with a viscosity that is suitable for lubricating the bearing under the operating conditions foreseen (speed, load) - not much higher because that would raise the operating temperature. given the required viscosity you will need a amount that will be able to dissipate the heat generated in such a way that the operating temperature more or less can be stable under the operating conditions - the amount of oil needed will relate to the surface that can transfer the heat to the surroundings. the use of cooling fins can reduce the amount of oil necessary.

to avoid frequently needed oilchanges you would keep the oil temperature within reasonable limits, preferably not higher then say 80 degrees C or somewhat lower.

the problem is of course that you would need to solve a equation with more unknown parameters to solve then you have equations available. a more practical approach would be to just do a experiment with the more common used oils (ISO VG 32, 46 and 68) and see what happens running the bearing under load and see which temperature you end up with. the oil that stays at the lowest temperature would be the preferred choice.