About using the hara/dantien instead of local arm/shoulder:
I have never seen the benefit. Most of those who talk about it end up one-side weighted and on the floor, or easily blocked and blown through...dang...there's that martial talk again!
The use of the shoulder is going to isolate the arm from a clean path of power through the body.
There are other more sophisticated things you can do in generating power in the hand from the hara/ground...say in one direction, while the elbow can generate a different force in an entirely different direction... and so on. There are various ways the hand itself can express power from different parts of the body. Some of that joins IP to IS and aiki.
None of that is going to work when the arm/shoulder is in isolation.
A couple of comments. What about a previous statement you made that there are other ways to generate power than using the dantien/hara?
A second comment is to reiterate what I've already said (and this is very easy to show/see) along the lines that I see/hear a lot of talk about people doing "internal strength" but when you take a look at it, it almost always devolves to a heavy dependency on shoulder/arm use.
Lee, the trick to a lot of these things is that until someone has become acquainted with a lot of these things (e.g., your question about hara, muscle-chains, etc.), they can't know that they're there or they can't conceive of them. Worse yet, a lot of people get a start along the way, but they feel too quickly that they're experts, so their learning becomes truncated. I've had a number of people, over the years, who had very few skills but a lot of pride stop me in the middle of some very diplomatic "maybe if you...." to say "Yeah, yeah, I know.... after all, I *teach* this stuff". So I don't say anything since they already know everything.
All of these factors add to the difficulties of the original question about paths that lead to internal strength.