Now I don’t really like nigel, stopped checking his youtube long time ago, never saw much of it either however. I’m don’t entirely agree with what your saying here.Nigel teaches beginners a lot of bad and counterproductive habits, particularly overly aggressive root pruning. His trees develop at a snail's pace because of this. This tree is 17 years old! Wut!
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from the picture, the trunk seems to have some taper, showing of age, no straight section and overall does seem to have ok ramification.
Is it a big tree well no, but I’m sure he didn’t intend to grow a big fat one but small shohin.
Could it be further along in 17 years? Perhaps sure but it’s definitely not an attempt you can laugh at. In japan you can find stuff like this too, or pines that are 10,15 years old yet less thickness then what they guys in the 6year challenge are getting already. Because it’s not grown for that purpose.
Different purpose, different techniques.
Some call it setback, maybe he exactly wants this restricted growth.