I always insert "after you have mastered the fundamentals" to that in my mind.
Yes that makes sense, I agree.
Though there are also sometime varietys of the fundamentals. Best example is vibrato. You absolutly gotta be able to do a vibrato well. Thing it there a different types. I can think of 4 of the top of my hat:
1. The classical vibrato where you move the finger horizontaly, not bending the string, but changing the pull and therefore pitch. Very subtle and sweet variant which works much easier on nylon strings, but I for one enjoy it a lot on electric too. Lacks for fast stuff though.
2. The normal we all know which essentially is a fast bending out of a hand motion. There are sub categories on this one too, but we all know what this is. I have only recently started to like / use this / be able to do it when it just started coming naturally.
3. The clapton where you basecally move the guitar and not the string by rocking the entire neck.
4. The Vai which is a combination of the classical and the normal (1 and 2) where he moves his finger in an eliptical motion. Strange stuff.
So while you are right, the rule also somewhat works with the basics imho. Yeah, you should be able to do a proper vibrato, but I think there is not a special one you should know, just at least one that suits you.
I am happy with my classical style so I hardly work on my normal and while I slowly improve on it too I actually try to make myself only use it very rarely.