why balanced power last before component?

Atma, instead of being troubled or suspicious, neither of which sounds like fun; why not turn your 'concerns' into profit?
It sounds like you have a solution for which the need is there. People are obviously spending (wasting?) money on relatively expensive Equitech products to cure the problem-as you describe it. Why not earn good money by tutoring all the designers (you infer there are many) in what you have said is the relatively simple art of proper internal grounding? Or, offer a custom service of rectifying inadaquate/faulty grounding schemes in noisy amps? Since one can easily spend $3000+ for one of Equitech's balanced power products I'm confident many owners would prefer to pay you to fix the problem at the source.
Again, if you don't know how Equitech ( the only one I'm familiar with) balanced power solutions for AC current effect a very significant reduction in line borne power distortions-which benefits the power supplies of ALL audio gear transistor or tube- you may find reading the Equitech technical information to be enlightening. It's interesting you find the problem of AC line borne pollution/noise so simple. I quote ANGELO BAGGINI'S book-HANDBOOK OF POWER QUALITY- "power quality is apt to waiver". Seems to be a huge problem for many. Also, if MARTIN GLASBAND doesn't know about balanced power-I'd like to know who does.

Atma, as a follow up, in Baggini's book there is a section titled
MONITORING POWER QUALITY. In it Andreas Sumper & Samuel Galceran-Arellano open by stating "power quality phenomenon are physical phenomenon that, in many cases, are APPEARING AND DISAPPEARING ARBITRARILY (not based on reason or evidence)." This arbitrariness is something that definitely bothers lesser designers than yourself; so it looks like there is a profitable business opportunity; perhaps a global one. Best regards, Peter.

I have found that designers in this industry often do not like being told that they have introduced a bug in their product.

The way you ground audio equipment BTW is simple: the circuit ground in the gear is kept isolated and insulated from the chassis. This includes the input and output connections. The chassis is directly grounded to ground through the AC cord. The audio ground is then referenced to the chassis through a resistance, one that is large enough to prevent any significant ground currents. In this way the equipment will not put any current though the ground and will be immune to ground loops.

Its simple- not rocket science, but you would be amazed at how many designers have not sorted this out. As a result there is a lot of snake oil out there dealing with the aftermath of poor grounding, and its not limited to high end audio.