I would disagree on some points. The reason new strains have gotten so much better over the last 10 years is the simple fact of the size of the gene pool is literally 500 times what it was in the 90s simply due to availability alone. Now I would fully agree 90% + should not be breeding and because of this lots of genetics have become muddied. However, what the top end does is use it is as building blocks as u mentioned. They take say a 91 Chem dog or the like and bx to its best expression ( if they are real quality breeders they will always bx a non breeder cut to stabilize). Then what they do is start building depending on the desired outcome. The massive difference between today and 30 years ago is what I mentioned before in the gene pool. The reason this makes so much difference is something called the entourage affect. When they create something with a ton of different genetics they will end up having sometimes 7 to 10 or more different
terpenes which science has recently shown to be the defining reasons for the experience of the end user. Whereas in original NL you would have had mostly
myrcene and pinene I believe and in small amounts. Some of the newest and best phenos have 3-5%
terpenes. NL had less than 1%.
Next thing to consider is absolutely nothing on the planet is unadultered. This is nature. Back crossing happens without human interference. Just living and dying in whatever place it naturally occurred. Meaning you would have had cross pollination happening all the time which would have produced seeds and that continued for literally how many hundreds of years if not thousands before a human ever harvested a seed.