A direct quote from one of his comments: "My current understanding of chi is non-supernatural and metaphorical."
The expression "[My current understanding of chi is] metaphorical." is far from the claim that qi is metaphorical. There is a clear semantic difference. And as a matter of fact some would claim that all understanding is metaphorical, and while discussing theory of mind is not totaly irrelevant to the initial subject at hand there is no real reason to digress further into this.
He is wrong because he says that chi is metaphorical and jin is a balance trick.
That is not actually explaining why he is wrong, just a statement that he is wrong and which statements you consider is wrong. You are not really explaining why he is wrong with that statement even though it uses the word "because". Nor did he actually use those words, you are choosing your one interpretions of his statements, which is not only rude but als bad practice in a discussion, you should instead quote him.
As I stated in an earlier comment, the correct explanation is that chi is tangible (though etheric) energy and jin is the concentration and projection of chi from the dandien.
Well first of all to say that qi is tangiable is a very much using the wrong word to desribe it, while tangiable can mean many things (and it could be used in certain deifnitions to describe qi) it is primarily not interpreted as something which qi could be described as. As such your choice of words are confusing at best, or more likely a fallacy. Secondly the usage of the term etheric makes litte sense, mostly because it doesn't really carry much meaning today except for usage in historical usages from either ancient greece or victorian philosophy, none of which makes much sense using modern terminology. In essence it means nothing here unless you are using a cosmology which is based on either indian, ancient greek or victorian ideas. If you are please specify which. Qi basically just means energy, and there are many categorisations of energy both in the west and in the east. Many uses of the concept of Qi in chinese are directly translatable to uses of the word energy in english. Other usages or forms of qi do not have a directly translatable concept in english, but these terms can be translated as an abstraction of something in the form of what in english would be refered to as an abstraction that is energetic in nature. In chinese martial arts (and especially in internal martial arts) qi often denotes a form of qi that is an abstraction of how energy acts in the human body, or how we aquire and use energy.
To describe jin as "the concentration and projection of qi from the dantien" is a total misconception of jin. Jin does not really have to coem from the lower dantien or any of the dantiens for that matter, jin basiclly just means force or power as used in western macrophysics. The misconception that jin "is the concentration and projection from the dantiens" likely comes from the amalgation of two things: Firstly that jin is (in most cases, but not all) most effectively used when it springs from the dantien out towards to where you wish to apply it. Secondly would be the confusion with the term jing, which is a complex subject on it's own and i won't digress further than to say that it is indeed connected to the lower dantien and is indeeed a concentrated form of qi and projecs qi aswell as being an important concept in internal alchemy.
I don't get why you've gotten so worked up because this explanation was present from the start.
I'm not getting worked up, i am simply trying to educate.