In the 18th and 19th centuries, a similar theory was popular that a variety will age and deteriorate with time and loss its vigor and productivity, and that therefore new varieties need to be produced all the time via crosses & seedlings. Of course, it’s a complete BS, since we know now many varieties (apples, pears, many stone fruits, etc.) that exist and have been asexually propagated for at least two and three centuries (and some more), and nothing happened to their vigor. For some varieties, a mother tree was known that existed 300 or 200 years ago, and all the trees of that variety in existence today have been asexually propagated from that mother tree via many generations of grafts or buds, and we still have young and vigorous trees that come from the same line and will thrive for many decades.
You don’t have to be Connor MacLeod and live for centuries to know about this, this is why people have books, so they can learn of what happened before they were born, and before their parents were born, and their grandparents, and so on. You can read, for example, “The Fruit Manual” by Robert Hogg, published in 1884, before my great-grandparents were born, and learn from it about a mother tree that was grown from a seed in the early 18th century, and still was known as an old tree in the early or mid 19th century, and we now in the 21st century are grafting the same variety in our orchards and observe vigorous growth of our young trees. And it’s not just one peculiar variety, there are so many varieties that exist for centuries through grafting or budding, and you can learn about them by reading books.
If you can’t learn from this widely available empirical evidence and believe in old wives’ tales instead, then all the development of the modern scientific method, starting from Francis Bacon who came with it more than four centuries ago, has been lost on you.