Since you refuse to learn the past, how would you know?
How do I know?
My reference text for the history of tailoring is Edward B Giles The Art of Cutting. I repeat: no texts on cutting from the 1300s exist. The earliest text based on some sort of mathematical method of cutting that Giles could find was by Juan de Alcega entitled Libro de geometrica practica quel al trada de toccanto officio de sastre Madrid, 1589.
Since your grandfather seems to have taught you how to apply Alcega's system, along with other even more ancient Medieval systems that are lost to time, perhaps you might like to explain to us why this archaic knowledge is equal to a modern system. Giles certainly didn't seem to think that these ancient systems were the equal of modern post-Wampen systems. I am sure Giles would have ridiculed any suggestion to this effect and might have likened it to thinking that the pre-Copernican view of the solar system with the sun rotating around the earth was equal or superior to the modern model on account of its greater ancient wisdom.
On P144 Giles states that Wyatt, 1820 credited the introduction of the inch measure and square to Mr B. Read. However, George Atkinson of 23 Castle Street, Falcon Square claims the credit of having first introduced them around 1799:
"I am well known to the trade, and can say without fear of contradiction that I was the first person who used the inch measure and square...I made an inch measure of parchment, marked it with inches, halves and quarters; I applied it and found it practicable. I considered a foot square would be useful in marking the cloth. I had one made: marked it with inches, halves, and quarters; this led to a square of two feet by one, which is the square in use at this time. From the use of the inch measure, the square, and great application, I reduced the trade of a tailor to a system. When I first began to use the inch measure, I was laughed at and ridiculed by the trade in general, as being of no utility...It is now 40 years since I commenced it, and I have the gratification to see and know that it is not only used in this country, but in every known part of the globe where we have communication."
Honestly, I think it exceedingly fanciful to think that if you regress to a methodology that even the Amish would find archaic, we would uncover such extraordinary ancient wisdom that the modern way of doing things (Victorian being considered modern) would appear to be little but foolish industrial shortcuts.