For the last 3 years+, around midnight I ask almost everyday 3-4 questions, about what I can possible eat the next day without too much problems(since from a very young I have a rare illness that makes eating challenging).
That is around 3-4 thousand questions just in the last 3 years, many asked around the time we would change it to fit True Solar Time usually(as that is the time Day Branch changes). With different day branch often the questions asked would be read in a very, very different way, so this is clear indication in many cases. Also the health changes are very clear to follow, as this is the nature of the problem.
Considering that, I have no doubts that we need True Solar Time, not only in BaZi, but also in Liu Yao. Only system that doesn't seem to work with it is Mei Hua and even there we need it at some specific cases. ZWDS also seems to need it, however the examples there are just 2 for me so far.
I don't want to post any examples, as I don't see the point, but in my experience I don't think there can be anything that can convince me we don't need True Solar Time.
And of course what Jung called synchronicity(while we often call "the flow" or "the process") is always working, so any chart of hexagram we read will have some relevance to the person/question, however that does has its limit if used outside of the cycles of change and the calendar. Also we are studying the changes, not connection with inner self/soul/oversoul/monad etc., the second have been much more developed in the western shools and while it can be very, very helpful, that is inner path, Five Arts can offer understanding of how change happens and that is still very needed in the west, but very, very different path to follow.