Soap and water + sponge will remove way more polish of a car than detergent free water, pure or otherwise.
Well anyone with half a brain doesn't use soap on their car! :

You use wash and wax.
Pure water is aggressive like you've said, it's not like tap water, it does take the shine off if it's rubbed in.
I've tried it, I don't see how you can argue it.
In fact I do know why, because just like a lot of others on here you think pure water is some sort of magic potion.
I'm still experienced in valeting, I do it all the time. 
I don't tell you how to play cricket, why tell me about valeting? 
Wash and wax may be your preferred choice, that doesn't make it the right one or necessarily the best one.
Why on earth everyone believes pure water is aggressive is beyond me, it is no more aggressive than rain water, and at what point does it become aggressive?
We measure our TDS in parts per million, I think ionics (I could be wrong) have a system that measures it in parts per BILLION!
and when measured like that, our water at zero parts per million is not pure at all!
As I keep trying to tell you Rog, I actually have a brain, and I'm quite analytical too.
I don't know the product make up of wash & wax, but it will have detergent in there somewhere, and any contact with cloth/sponge/brush and dirt and grit will have the capacity to mark paintwork.
Pure water alone or used with a brush is not going to dissolve or be responsible for the spoiling of a waxed finish, certainly no more so than ordinary tap water.
The wax on a car will of course wear away from the surface if rubbed, and will also wear away with natural weathering, hence why you will reapply it regularly.
No wax is going to be as hard as the paint you are applying it too.
and i have not at any time told you how to valet a car, but that doesn't mean that I won't offer opinions on your statements, and just because once upon a time, many years ago, for a short while you valeted cars for a garage does it makes you the forum expert on car valeting, from other posts I've read, there are a few on here that have way more experience in that field than you do.
you of course cannot offer much of an opinion on cricket because you neither like the game, play it or understand it.
Ian