Rockvirgo, yes to a point. But for this "shearing" action to be of benefit, the lubricant has to be strong enough to handle the load imposed on it by the two mating surfaces so that the surfaces DO NOT touch, but are in fact sparated by a continually shearing liquid. That is why water is not a very good lubricant, even at medium low loads. That is why a minimum viscosity is necessary for a lubricant to be successful.
Also, synthetics, as you have pointed out, have long straight chain molecules as opposed to the conventional oils which have a mixture of ring and branched chain along with some long chain molecules. Its not so much the molecules breaking up that is the "shearing" as it is the separate molecules moving against each other. Long or straight chains tend to slip by each other more easily than branched chains.