I skipped the handful of exceptions because they have no rules associated with them, you just have to memorize them. Yes, it would be 3 if I counted exceptions. I am aware that they exist; you can check their list at the end of my post.

>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.

I must have been unlucky. I don't remember what resource I was using but it was primarily teaching with a separate table per suffix. Maybe the pattern was called out but I missed it due to feeling overwhelmed with the tables.

>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.

That's fair — if most people don't stumble here because this is clearly explained, that's good, and it means I've overstated the "usually taught". I still find that I prefer the specific style of explanation where we consider the corresponding vowel a part of the suffix, like -(i)masu or -(a)nai, which is how some linguists view it. That is another part of the motivation for writing the article.