The bottom line then is that the better the muscle-tendon channels get developed (connected) through systematic practice, the more dense the connections will become through the whole abdominal area, and the more one can control and direct connected whole-body power from the centre of the body.
wouldn't agree with what is being called "whole body power from the center of the body"
any point touched can have its own center, and be acted on from there.
It's a different way of managing force using a different system to manage it with along with a different idea.
Anything that strengthens the muscle tendon connections would be called external, anything that helps to develop an awareness of the
bodies connectivity in this case through the connective tissue ie "stuff" is starting to train and develop the body/mind in an internal fashion.
The question might be better addressed as to why? whats different?
one way of checking is how one feels a force applied or received.
For those I work with we make a distinction between using force, and not.
In this case force being derived in the normal sense though the normal mechanisms
with what is called no "force" its not felt but the other person is moved, or in the opposite case
a force can be applied and also not felt the person is very stable. This involves no tension.
To the degree that one can do this is a good indication of level of skill and understanding.
This is only training a skill, the usage and application is something that also needs to be trained.
Something that seems to be lost on some, sometimes with bad results
what is called "dantian" rotation is quite literal in description not really true anatomically.
In the groups I work with there's a couple of other concepts that have to be developed before this comes into play.
Here in the discussion it will be and has been IMO confusing for some, because they seem to be talking about different things relative to how the body manages force, and how it can be used on another body.
I would start by saying all force felt, is from ones self this is the normal way and how the body/mind manages and responds to force.
Once one can get past this, a lot of things should become more clear.