DY in Chassidus we question why things are the way they are all the time. And since asking “Rebbe help me with…” Can sound like the same idea as davening, because only Hashem provides us with our needs, why is it OK to ask a tzadik to daven for you or even to help you, as yidden do? That’s what the answer is addressing.
As far as kol yachol, if you look it says yachol hakol, not kol yachol. Yachol hakol means the Rebbe can do anything. Which is true. A tzadik, by connecting himself to the power of Hashem, is not limited by nature, and can do the impossible.
I personally know a woman who the doctors said can’t have any children. Physically. She got a Bracha from the Rebbe and had 15.