BJJ Overly complex?
It is all about learning to move in relation to what the other person is doing. Much like push hands!
Cept you are on the ground or in a clinch typcially against someone that is really fighting back with everything.
It does look like a series of very complex moves when you first engage it. What I found though is that it really is about the appropriate response to a input from your opponent through proper alignment, positioning of your center etc.
I rarely think about "moves" or "technique" To me, it is much like aikido except it is at a different range. Probably why you found you did so well with it.
Your experience parallels mine. I choked a few guys out with little or no experience in it. To be honest, the first time I experienced it, I choked the guy out and dismissed it as being something worth studying since it seemed so easy with only my aikido background. A few months later, I was taken to school by a few other guys that were a little better. Opened my eyes!
If you label what we do in aikido as typically being internal...I would agree with you, they are very applicable..just a different range and set of conditions that you need to further refine to be proficient at that range.
Conceptually I don't separate internal and external or objectify the whole ki process..it all simply rolls into proper body mechanics and principle of dynamic movement...they are universal and learned from repetition...doing the same correct thing over and over and over until you finally figure it out.