Scrolled to a random position in the file, and there's 37 lines of all declinations of the word "monologue". Followed by a bunch of nouns with just two to four forms, followed by 47 declinations of the word "monopolise".

What he did is no small feat. You still have to memorize which suffixes are possible in which verbs (there are rules he would pick up on, but there are exceptions to the rules). But it is made easier by French verbs having a lot of possible suffixes, those suffixes being fairly regular, and English taking a lot of its "fancy" words with French (or adopting a Latin version that's close to what French adopted from Latin).

I still couldn't come close to thinking about achieving it. He is doing the extreme sport version of scrabble for sure.

And these advantages in French make it even more impressive that he could do the same even in Spanish.

I actually don't think the exceptions are much of a problem overall. Most irregularities in a language happen with the most common words. Once you go from learning the most common words to simply learning all the words, the relative frequency of irregular formations that you encounter would go down dramatically.

98% of those words are useless for competitive Scrabble.

he knows them anyway