the problem is, it's not theories, it's a method used with good results by a lot of people (including me), you don't believe it but it works, because it is not "obvious" (if how plants grow was so obvious, there wil be no need for science working on it), and your reasoning about more growth = more thickening is not entirely true (at least it's not enough to explain thickening), the total lenght of the branch and the arm of leverage it puts on the attach of the branch (mechanical stress) is a decisive factor in the thickening of the base of the branch. By removing side branches, the branch lengthen much more than if left to ramify naturally, because all the push or growth is concentrated in the apical shoot, thus mechanical stress on the attach is stronger and then the tree deposits more wood on the base of the branch.
You have not proved anything either... cause you don't have controls...
I think that
@MichaelS is right. It makes no sense that removing side branches will increase growth/thickening on the main brach/trunk section. You're removing and reducing everything (hormones, sugar production, floem and xylem transport, water circulation, everything. You need a stronger (and thicker) structure to support a greater biomass. Also, more branches = more drag. Some people say that is the bouncing of the branches in the wind that makes them thicken...
i think one of the thing making people not understand this technique is that it is not so much about more wood production (in terms of total wood produced the more growth more wood is most probably right) but rather WHERE this wood is deposited to support the branch (because only the base of the branch will be kept in the end), and this is what achieves this technique, having the most wood deposited at the base of the branch
I think it is you who is not understanding. So you're saying that having a main brach with a 10 more side branches will not thicken faster at the base of of the main branch compared to a single main branch without side branches? Hard to believe...
Again... why do we thin shoots down to 2 arising from the same location? It's common practice right? No one questions this... Think about it.
PS: not all the great bonsai artists are with this theory. I remember listening to Ryan Neil in one of his free videos (I can't remember which one) that it's foliar mass that drives branch thickening. And guess what: he was taught in Japan...
This is a very simple experiment.
Grow 10 individuals from the same species from seed. In half of them, you continuously cut side branches as they appear. The other half you leave untouched. Otherwise, all equal. After 1 or 2 years (or more if you want), measure the diameter at the base. Also, cut all side shoots (in the control) and weight everything...