Honza - - if I may - - I would like to offer a few tidbits for consideration - - gleaned from various teachings and personal experience. Not necessarily "opinion" - - but is probably more safe to offer it as such.
What you ask for - - that metaphysical laws be determined / proven for all - - goes strictly against the intent of the Path itself. There is an old principle that states that no spiritual principle / law can ever be proven via physical means. There are reasons for this - - and I will outline a couple here.
One of the biggest reasons is that the physical world is one of effect. So - - when various scientists / metaphysicians try to understand the world about them, they are basing it all on effect - - not cause. They - - in a sense - - become an effect of an effect. Which is one of the most insidious traps one can find themselves in. And when they try to interpret a psychic experience via physical perception - - that just doesn't work either.
Another reason for this not becoming clear to and for the general population at large is because there is an inherent and necessary need for the element of "faith" in the discovery of life beyond the physical. Physical proof - - would destroy that. "Faith" can play a big part in ones discovery of Truth - - all the way to the "end" - - so to speak. In ways not necessarily clear to most or obvious to many. Nothing against them - - at all. It's part of the Path - - part of the discovery of it all.
But - - these laws certainly CAN be discovered - - and the answer lies in your own signature at the bottom of your post. It is *your* relative and conditional reality that will eventually uncover everything - - of and within all levels of Life Itself. That is why the Path is an individual one. Groups - - do not grow uniformly as a group. Individuals within the group most certainly advance to the extent that they can. But the Path is an individual endeavor to understand just your inquiry. And Soul begins to make sense of the metaphysical laws and uses them to advance It's own liberation thru service and effort of and within Life Itself.
One slight clarification - - and you can take this with a HUGE grain of salt - - but the metaphysical laws are not - - "spiritual." The metaphysical laws are psychic. They deal with the worlds of duality - - the physical / astral / causal / mental / and etheric worlds - - where the elements and "things" within each massive dimension / plane are made "real" only in relation to its opposite. This - - (and again - - take this as you wish) - - is the nature of duality - - and has little to do with "separation" - - as many metaphysical teachings would have you believe. No doubt - - there is a HUGE factor in wrestling with separation - - as the mind would have you perceive it - - but this is not a "definition" of duality itself.
So - - do not give up hope. You can personally go out and solve / resolve an understanding of every metaphysical law known to and by - - Life. And then you can continue on into the spiritual nature of IT all - - which is beyond the worlds named above and would deal more with the "essence" - - or "spirit" of the understanding of life if you will - - the "abstract" of it if you will - - rather than the psychic nature of it all as it deals with the duality of things. And by duality - - again - - I mean - - that high cannot "exist" without a low - - that cold cannot "exist" without a hot - - that mountain cannot "exist" without a valley - - etc.
If you could NOT go on by yourself and prove all of this to yourself thru direct experience - - then the entire Path would be just one of ongoing futility. I assure you - - it is not. But you are most correct in assuming that the Laws of Life - - of which the metaphysical laws are a part - - are very real indeed. And - - if you consider the old saying - - as above, so below - - then the metaphysical laws would be "more" real than the physical - - and the spiritual laws would be "more" real then the metaphysical.
Which - - holds true.
Again - - consider all of what I said above only for what it means to you. Many would find tremendous resistance and defiance in accepting what I just put forth.