Concepts are great
In general, I agree: concepts are the underlying part of all jiu-jitsu that works. Posture, base, leverage--these will be constants across all techniques that work. I think Kit goes off the rails by extrapolating from his experience to advice for the general populace, however. For instance:
One of the things I noticed early early on was that you didn’t have to drill something 100 times to be able to apply it during training. If I understood the basic principles of a movement and winged it, it would usually work.
I've experienced this too, with a certain small set of techniques. But I'd argue that a lot of students can't do this with most techniques. It relies on a lot of rolling time and a large helping of natural athleticism. I have sweeps that came "naturally" to me after merely seeing someone demonstrate it on video, but I also have sweeps that were total garbage until I drilled the hell out of them under constant supervision from a coach. The proportion of techniques that fall into one category or the other will vary according to each student's athleticism, intelligence, and learning style.
Techniques that "work"
I'd also like to hear some examples of what Kit speaks about here:
I remember using moves in sparring that I had never practised before and getting them to work. Even ones I had been told were “bad” by the instructor. My reply to him was always the same: “But it works”.
Were these strength moves, or techniques his instructor just hadn't seen yet? Marcelo talks a lot about moves that work against opponents smaller than you, or even your size, but that fail against someone bigger or stronger. Why practice those techniques?
Some techniques work, but are lower-percentage than other techniques.
Techniques AND Concepts
Rolling is always going to be the ultimate laboratory for finding truth in technique. But to advocate for no drilling is to throw legions of athletically cursed individuals into a pit of despair. I prefer instructors who teach specific high-percentage techniques as instances of general concepts. For example: "Here's how we're going to learn to pass the guard today. Notice my posture, here and here. Posture is always important and this position is a fundamentally strong posture. Notice how the important part of this technique is a particular kind of timing. This timing will work for lots of techniques Notice how this is one of five maximally efficient ways to pass."