Would it?
I tend to wonder that if there was a shortage of pathologists, that would INCREASE the tendency towards consolidation. More mega labs. More mergers. Fewer pathologists would mean fewer experts, and mega labs could pay more to bring them in, and further consolidate their power. If it's hard to find a local qualified pathologist, what makes you think that clinicians wouldn't just find the easiest way out and go with the mega lab that promises the best turnaround time (and sends people out to their region if they need it)? It may also increase the use of technology such as slide scanning, etc, to make things more efficient and centralized, and increase the tendency to bypass local pathologists.
Of course, this might all be wrong and you may be totally right. But I don't think it's as obvious as you put it. But I fail to see how it is obvious that if there were fewer pathologists, there would be more partnership track jobs. Sure, glut of pathologists means some groups can afford to hire employees instead of partners, but a shortage of pathologist might mean that that group can't competitively bid for the business, which then gets taken over by a larger group (or the larger group pays them to just do what they can, since they can't handle it all).
What the business world shows is that when there are many people doing the same thing (oversupply), mergers tend to happen so that some people can consolidate their efforts and increase their competitive advantage. But when there is a shortage (monopoly), it becomes much harder for the little guy to gain a foothold. The monopoly just steamrolls everyone.
I think the reason pathologists are doing more for less is because of the less - less compensation means people have to work harder to maintain income. This is a direct reason FOR the oversupply of pathologists, not a result OF it.