Pretty much every greatly respected historical thinker of our history who advanced human knowledge was also dead wrong. What was known to be scientific fact at pretty much any point in history - including, I absolutely guarantee you, right now - is seen or will be seen as ridiculously and self-evidently wrong a few generations later to an extent that it can be difficult to believe that someone that was seen as a genius of their time believed in such fatuous bullshit. That Decartes, eh? Light being made of 'corpuscles'? What a twit.
Teclis' model of magic is great at explaining the kinds of magic used on Ulthuan, but of course it's going to fall apart when you try to make it apply to all the kinds of magic used in the Old World. Similarly the theories of the Old World would fall apart in an instant if you carried them over to Cathay and tried to make sense of the Lores of Yin and Yang. Nagash's legacy lives on to this day because he managed to build a build a form of magic that integrated a whopping two completely different paradigms. This is why you can only get a +5 bonus from the books of any one culture for any one subject, because at this point nobody is going to have a framework that is going to be anywhere close to universal.
The wisest of all knows that they know nothing, but scientific nirvana is bad at building siege weapons. The gaping flaws in Archimedes' grasp of physics came as no comfort to the besiegers of Syracuse, and that Teclis was unable to fully explain the magic of the Kurgan did not stop his teachings from killing a great many of them in Kislev.
