I fully agree, it would be nice if:

-the map fit on a 1920 pixel width monitor

-the small version had a readable font

-it existed out of colored regions with the name of the dialect inside the region on the map rather than different types of legends everywhere

Fascinating topic, but the presentation ... well, let me just offer Edward Tufte as a resource:

https://www.edwardtufte.com/tufte/books_vdqi

This one is much easier to read: http://robertspage.com/dialects.html

And, at parts, also more interesting. Even if not as detailed.