I suspect a tremendous amount of selection bias in this, affecting what we remember (and don't) about our birds. Its human nature, and can serve to reveal a bit about our unconscious beliefs.
That said, its a fact that certain hybrids produced at commercial scale have been selected for egg laying - by the big breeders who want lots of production, and by the buyers seeking those birds out. There is, for at least those breeds, significant selection pressure (as the professor said) for some "quantity" birds that individual consumers might benefit (or suffer) from. Moreover, the quantity of birds most of us will own, over our lifetimes, allowed to mature to old age - set against the number of birds sold yearly - is a fraction of a fraction of a fraction of an infinitesimally small fraction of a percent. None of us is likely to have the personal experience to offer a statistically valid opinion - our sample size is too small.
What we can do, however, is evaluate the categories.
I don't see how its possible to lump "breeders" into a single category - as the posts on BYC make clear, individual "breeders" run the gamut from backyard hobbyists of no particular knowledge or experience to industry respected specialists in a line (or a few lines) of birds.
To use myself as example, I am, arguably, a "breeder". My flock breeding goals have very little to do with longevity, except as a potential consequence of being hearty free rangers with decent weight gain early on. Likewise, if they aren't as prone to reproductive problems in later years, it will be only as accidental consequence of my willingness to give up some frequency of lay while getting more meat on the bone. Neither is a deliberate effort on my part - I'm not breeding show chicks or pets.
Obviously, others will have differing management practices, differing goals, and their selection choices will result in differing outcomes. The professor offers one such above.
Unlike hatcheries, whose commercial breeding goals largely align. Additionally, as some posters noted in threads earlier this year, some hatcheries have drop shipped birds to end purchasers which originated at other hatcheries. And hatcheries seem, in some cases, to be obtaining their stock from certain (likely shared) large breeders.
That significantly reduces variation - but also raises the real possibility that your Privett Hatchery Stock or ideal Hatchery Stock of a particular breed might be exactly the same birds as Joe the Breeder's large flock of particular rare breed.
So while I think we can make some very broad statements for a couple of the high volume "breed" lines, I don't think that statement offers anything of use or value regarding an individual purchase of a bird at hatching, unless you have specifically selected it or its known individual parentage.
