First of all, there are very much peculiar forms of Daoist meditation. Inner alchemy (neidan) is the most notable one; where you observe and imagine your inner organs and layout. I doubt you've done any real Daoist meditation, but its not a surprise as these methods are very rare in the west. Taichi isn't meditation, its just a set of physical exercise. The fact that you talk about brain at all suggest to me that you never actually had a proper instructor teaching you how to do Daoist meditation in the standard way (nor read any authoritative Daoist or Buddhist manuals on meditation, because all of them are fairly mind centered, most denounce physical reality altogether); and no I'm not just talking about a religious believe, how you perceive and cling to things in meditation affects the result. Nowadays too many people think they are innovative by applying biology and physics theories into their meditation, which defeats the entire purpose of insight.
If you are talking about Daoist and Buddhist meditation, get that physical function of body and brain out of there completely. The first thing a qualified Zen teacher would do is to smack you out of over-theorization of these concepts; they are nothing but hindrance to Satori (wu).
Um- what the heck do you think 'Internal alchemy" is about if not using the mind to alter the body? Really? You can actually write such a self defeating retort without realizing you just contradicted yourself?
I could really give a dang what a "qualified" zen teacher would do. Number one- I've practiced taoism for 46 years. I was an assistant teacher of Tai Chi. Number two. Just as with Buddhism, the history of Taoism is the history of a fairly simple philosophical view that became embroidered with all manner of magical horse puckey over centuries of people trying to figure out a way to make a living at it. The initial and valid insight was buried.
Tai Chi, itself was a very late addition. Buddhism has variants with demons, angels, and all manner of magical delusions that various peoples decoupaged on top of the fundamental teaching. So too, with Taoism.
Later "Taoists" practiced internal alchemy with the intention of living forever. That is the same sad dodge of mortality as heaven or rebirth that every other 'faith' dredges up... except with the Tao it is entirely opposed to the actual central concepts of Taoist Philosophy.
This is a common theme in human ideation- that they tend to fantasize and re- invent and often reverse the original concepts, because human beings tend to be drawn to certain kinds of narratives... and because those narratives are an easier sell, they then tend to take over as a form of belief.
For example. Jesus claimed he was the Son of Man. He denied being the son of God. His core teaching was not that we are all sinners, it was that anything HE had accomplished, ANY person could accomplish and thus you could become truly SIN- FREE.
His Dharma was the perfectabilty of the human spirit. But within a few hundred years, Jesus had been made into an incarnation of God... and God Split into 3 separate magesties... and a host of lesser demi-gods enshrined as saints. And humanity converted into inveterate sinners who could not attain heaven without the forgiveness that only the church could offer.
Coming from a teacher who believed there was only ONE God and that any man could learn to Sin No More. ( this is why in certain Buddhist traditions, Jesus is seen as an avatar whose Dharma was lost )
What I was referring to was that, unlike buddhism, there is not one single mention of anything even remotely resembling meditation in the foundational texts of taoism.
And while you can jerk around with such later embellishments as internal alchemy- ( Like I did) they do not serve the same function as meditation. Internal alchemy is an Egoic exercise. And as such, in my experience it fails to teach what meditation is meant to teach.
As to your suggestion that modern science defeats the purposes of the insight... the Dali Lama entirely disagrees. He has stated that in any area where Science disagrees with buddhist doctrine, then buddhist doctrine must be wrong.
I would venture to say that he might understand the purpose of Buddhism better than either of us.
After decades of spiritual study and practice, as well as a keen interest in emerging real knowledge of how the human brain and body work, I had to face the obvious... peoples who had no idea how the world really worked nevertheless had experiences and insights they wanted to express... and to do so they invented the answers to which they had no verifiable means of access as a form of narrative that others could follow. A finger pointing.
Sorry- speaking as a guy who mastered manipulation of it, there really is no Chi... Its just a narrative trying to make apprehensible something that is true about your body and mind... made up for the same reasons westerners invented "Humours".
That is, traditional techniques of manipulating Chi DO WORK... for some very limited purposes... it was a narrative invented to explain something you CAN experience... But, no, it doesn't do everything that narrative claims it can do, and no it isn't really working the way they claim it works.
Accupuncture does have some effects, but... no, it won't cure disease. And much of its perceived effect in wider purposes than pain management and muscle spasms is placebo.
internal alchemy and kundalini can prove to you that your brain can exert control over autonomic functions. But its not gonna make you stop aging and retention of semen will actually make you likely to get prostatitis.
If anything- frequent ejaculation is associated with greater longevity and vitality.
Crystals and astrology do nothing and mean nothing.
After decades of practice... and the application of a genuine intellectual honesty, I had to face up to the simple logic that ALL of the various ancient traditional beliefs claim to be the one TRUE picture of reality... and that by definition that would mean that only ONE of them could be right, and yet not one of them offers anything so compellingly more effective that it can prove itself the one true faith.
However- they Can ALL be equally wrong. Thy Can all be exactly what they appear to be- primitive attempts to explain something that they did not have the tools or science to adequately examine.
So- far from my analysis defeating the purpose of the original beliefs, it is quite the opposite. I seek to RESTORE that portion of each original belief system that shows evidence of being valid, and to nderstand HOW it can be valid in light of actual knowledge we are gaining about the human body, mind, and consciousness.
Of all the Original ancient beliefs, only TWO, in my view, have stood the test of challenge and modern science without being proven erroneous. The original texts of Taoism by Lao Tzu and Chuang Tsu. And Stoicism as elucidated by Zeno and Epicurus.
Neither bothers itself with any form of "afterlife" . Rather they seek to understand Life and being as we Can know it.
Strip away the malarky in other ancient traditions- such as the supremely complex Hindu mythology, and you find much the same basic insights into perception and being in most of them.
But my argument is that if you really want to get what is of value out of ancient philosophy or mysticism... you really have to try and tear away all the generations of false embroidery and facade that people who really did not understand it laminated on top.
(ETA- In my view it is truly sad that people studying such beliefs fall in thrall to the narrative, and entirely forget about the core concepts. Your post amounted to some form of "Purity Test" about whether I correctly parroted the catechism that is Currently in vogue or that You imagine was the 'ideal' form of the belief. Zen Buddhism is what Taoism DID to buddhism as it spread across China. As beautiful as it can be, i do not entirely agree with the Rinzai school- which is the closest to Taoism.
Karma, for example, is a great way of pretending that people pay a price for evil and are rewarded for good... which is a narrative the downtrodden WANT to hear... but it has no actual bearing on real life...or actual suffering. What I like about Taoism is that in its original form, it made up nothing. It told no story about the mechanics of being. It simply dealt with perception and our individual responsibility for what we think about what we perceive.
Real spirituality has to be in agreement with what can be determined to be real.
and the Narratives, the traditions are nothing but the MEANS we use to convey the realization that matters.
As Chuang Tsu wrote- once the fish have been caught, the nets can be put away.)