Perhaps this is true to some extent, but you must admit that how strong they are in game mechanics shows some part of how strong they are as members.
Besides, what makes you believe that Xaldin was much weaker than Xemnas? Simply because of his rank? That means absolutely nothing, as already stated in this thread.
Also, the person that I was making this statement to was calling Saïx the strongest, and they probably did mean in term of game mechanics.
Who's to say that, outside of game mechanics, Xaldin isn't the strongest member, or Roxas? Or any of the others, for that matter. The way they joined, and the order in which they died is not a true indication of their strength or power.