The straw man is how you claim it is usually taught. You claim that only 2 groups are taught when 3 get taught. You claim that you are given arbitrary tables to memorize, but it's usually explained to foreigners that you replace the last romaji to i when conjugating the verb into -masu form.

So in essence this article boils down to someone claiming that the usual explanation is confusing and then their own system turns out to be equivalent to the usual way it is explained.

And based off your comment here the reason behind doing this may be you extrapolating how you first learned it to how people usually learn it.