There is another factor that is rarely discussed. It is discussed here,

The best bicycle bearing grease

Lithium complex grease (lithium grease EP) – lithium grease built up to withstand extreme pressures. More resistant to washing with water and has a greater temperature range than ordinary lithium grease. However, the drawback is that it is a bit “too slippery.” Literally. It is easier to drip from the bearings and it can provide too little friction, so that the balls within the cups do not have enough resistance to spin around their axis, but they can slide along the walls of the cup. Therefore, uneven wear of balls occurs, so it turns out that the superior grease does worse in practice. A good example how the best solution is often not the maximum, but the optimal one.

Molybdenum disulfide grease – excellent for very high loads at low speeds. Forks bearings (shafts), which only go up and down, are the ideal candidate for this grease. In bicycle bearings, the addition of molybdenum disulphide does not bring any advantage. It can be too thick, or too slippery, in any case more expensive than ordinary lithium grease, without apparent benefit.

(Reading this Bikegremlin.com entry, along with the comments below it, it seems that the writer does not have an extensive background in this field, unlike some of the chemical engineers writing elsewhere. And some of his points may be mistaken. Still, he raises some interesting issues that are rarely covered, and some of them may have some validity. It may be that some lubricants are too slippery for some applications, including bike wheel bearings. Or it may not be. Further information and evidence might make it clearer.)