That said, some things where higher quality back then. For example modern fast growth wood is far lower quality let alone things like particle board.
One reason for this is that in larger trees, the rings themselves play less of a role in causing warping. Another is that many trees that make it to 50 years in a modern forest wouldn't have made it to 400 years if left alone. Old-growth forests have much greater spacing between trunks as the overgrowth trees that were successful outcompeted their neighbors; to have survived 400 years indicates a tree that was given superior placement and nutrition.
Finally, when trees are much older, they are much larger. This means that relatively more of the wood comes from the center of the tree, where there are fewer knots, voids, inclusions, etc. The moisture bearing part of the tree is on the outside, and in many species is unusable, so you have a much higher uniformity and yield in board feet from a bigger tree.
I feel like this plays into the popular idea that everything in medieval times was poorly built and covered in shit. We seem to want to think that because they lived in a largely illiterate, Church dominated feudal society that all the peasants were too stupid to function. That these savages would be too dim to possess the critical thinking skills to realize that if they used well built tools, that they could accomplish their work faster. That after thousands of years of human advancement, we hit this period where everyone not just lost accumulated knowledge, but forgot how to be a human in the process.