Adults don’t have to go that route though. I learned all the kanji from daily use through college level (some 3,500 or so) in a few months of study. You might as well point to the massive number of root vocabulary English has and make the same argument that English would be crazy difficult to learn (and you’d be equally right).

That has nothing to do with learning English.

It’s based on the premise ‘as an English speaker’ these languages are easy to learn. But, if your native language where say Dutch you get a different list than if your native language is Japanese.

That table is ranking languages by how easy they are for an English speaker to learn -- that is, how much commonality they have with English. It doesn't make any claim about English having some fundamental property that makes it easier to learn.

That table is expressly from the point of view of an English speaker; I'm sure it would look very different if written for Arabic speakers. Since it's largely a function of similarity to your native tongue, how would we even measure if a language is easy or hard to learn?

And what counts as "normal language classes"? Until at least high school in the US, every class other than math focuses on reading and writing.

Dutch and German are classified differently (cat 1 vs 2). But it is a well-known language gimmick of these 2 specific languages that when a native speaker of one of these languages speaks slow enough, a native speaker of the other one can understand him reasonably well. So where do these 6 weeks of extra work come from?