Jon also knew that this powers were in power order, so the first one, the mentalist, was the most powerful. He asked why to the stone, before choosing it.
The answer was simple, it was the only mental power, with it one could control any number of weak-minded (in comparisson) AND also becomes more powerful the more time one survive AND also it's transmited to the children, but, even thought the would be even more powerful, they would be infinitely loyal to their biological father without questioning it..
So Jon choosed it, without asking before why if one of them was more powerful, the others also drained the entire stone's energie...
