Xue Sheng
All weight is underside
I don't think you're wrong in that ki = qi, or that dropping ki and sinking qi are the same thing, I think they're identical, just in different languages. I just don't think of it as an internal system but a synergy of body mechanics ( posture, relaxation, position, balance, etc.), the laws of physics, timing, and intent. I think it's more a matter of what we believe qi/ki to be that is adding to the confusion.
In CMA to properly use Qi you need to have proper posture and be relaxed otherwise bad alignment and muscle tension impede the flow of Qi and make your movement more based on external muscular strength than on Internal power aka Qi. I think, or at least this is my view, that is it is a pretty simplistic system that we here in the west tend to over complicate and over analyze it, but that is to be expected since we really have no concept that is like it in western medicine or science.
In Taijiquan (Or at least my branch of it – Yang style from Tung Ying Chieh) you need Sandao which are 3 important tasks you need to practice Taijiquan properly and they must be worked on first before you start working with Qi.
First one must complete your Shen (Spirit – not religious spirit more like mind) and you must unify your Shen with the movement. Second you must make your Yi (thought, intension) an important part of every move and third is Shi (posture, position) it must be correct and comfortable.
Without these you cannot be relaxed and you cannot use Qi properly in Taijiquan.
Then, since Taiji is considered an internal style you get to Yi, Qi, Li; Yi moves Qi and Qi moves Li. Where Li is muscle but without Sandao you never get to Yi, Qi, Li.
Qi is Qi that is all if you talk to my Sifu or my wife (OMD) it is simply internal energy. That from my wife’s POV if you have strong flow of Qi you are healthy, weak flow of Qi you are sick and no flow of Qi you are dead, body mechanics does not really enter in to it. From my sifu POV it is much the same except you can use Qi to move and it generates more power than simple muscle contraction and in order to do this you need to have Sandao which includes proper body mechanics. But if you have too much muscle tension and qi flow is impeded and without Shen, Yi, Shi you will have to much muscle tension. I will add that both my sifu and my wife are born in raised in China and Qi is just accepted as what it is, energy. There is not a whole lot of debate about Qi as far as definition as far as they are concerned.
Basically you cannot sink Qi without Sandao it just will not happen, you may think it does but from my perspective it can’t. You cannot force Qi to sink.
I agree with you that body mechanics is important but it is through the proper use of body mechanics that you are able to properly use Qi.
Now again I will say I am not an Aikido guy, I have sparred Aikido people but I have never trained it so what I am saying may not apply to the Aikido way of thinking. It also may not apply to the Japanese philosophy and way of thinking that Aikido comes from since I am talking from the perspective from which I learned and that is Chinese.