I don't know what you mean by true heritage or purebred chickens? There have been threads on here where different people would give their ideas on what they mean, but it seems that there are a whole lot of different interpretations.
Some people would have you belive that all hatcheries are identical. They are not. They are managed by different people with different expertise with different goals, other than just to make a profit, of course. I'd consider profit a common goal. Some hatcheries have their own flocks and select their own breeders, some rely on outside contractors to provide hatching eggs, and some drop ship, which means they get their chicks from different hatcheries instead of hatching their own.
In general, the hatcheries use the pen breeding method, which is a way to mass produce chicks and keep the genetic diversity up. Think of this as a pen with 20 roosters and 200 hens randomly mating. You have no control over which specific rooster mates with which specific hen, so you don't have as much conformity in the chicks. When you understand that breeders of show birds that very carefully mate a specific rooster with a specific hen still get a whole lot of chicks that don't meet the Standards of Perfection, you can see that a pen breeding situaton has very little chance of producing chicks that will meet those standards. I don't know of any hatchery that even comes close to to regularly producing birds that meet the Standards of Perfection. Some are better than others, but the pen breeding method is going to make sure you don't get many that will not have some disqualification. Their prices also reflect that they are breeding for the mass market, not show quality chickens. Sort of like getting a pup from a pet store versus getting one from a championship breeder.
Each flock that has been inbred becomes its own strain. The skill and goals of the person selecting the birds will determine the traits in those birds. I recently read an article where someone had split a flock of purebred birds. From one of these flocks, he started selecting the large birds as breeders. In the other flock, he selected the smaller birds. I don't know how many generations it took, but he would up with two purebred flocks with the same ancestors where one flock member averaged weighing 9 times as much as the birds in other flock.
I can tell a clear difference in the Speckled Sussex from Cackle and Meyer. They have different people selecting the breeders and there is a clear difference in the results. But I have not gotten any from either that I would take to a show.
Some breeders are only looking to win a grand champion ribbon. They breed strictly for the traits that you see in a show. Others do that but also breed for the traits or characteristics that to me make the breed "heritage". These include things that are not judged like egg shell color, rate of laying, rate of growth for a meat type bird, things like that.
You really need to know what you want. What traits or characteristics are you after? If you want a chicken that is eye candy, looks pretty much what the breed is supposed to look like but has some flaws, will lay well for the breed, or is a good pet, then the cheaper hatchery chickens may very well suit your purposes. If you want a show chicken, then you need to find someone breeding for show chickens. If you want a chicken that could be for show but also has certain "non-show" traits or characteristics, then you need to find a breeder that is breeding for those characteristics. The key is to know what you want first, then the challenge is finding someone that produces that.
I'm not sure if this answers your question or not, but I'll get off my soap box.