Faith to be healed must take into account the fact that God does not always heal so it is subject to His perfect will.
Did Paul have faith to be healed of his thorn in the flesh (body) -- his infirmity? Absolutely.
Did God heal him? Absolutely NOT.
Did Paul have faith to be healed of his thorn in the flesh (body) -- his infirmity? Absolutely.
Did God heal him? Absolutely NOT.
You state that it is a fact that God doesn't always heal, but such a "fact" is based upon personal experience and not God's word which declares that everyone who came to Jesus in faith was healed. You say that it is factual that God doesn't always heal, but the correct statement would be that not everyone is healed in their subjective experience in relation to their own preconceived ideas about God and healing.
Faith can only be had by comprehending His perfect will, otherwise it is only hope. To discourage faith by saying God doesn't always heal as a means of consolation is a compromising of the truth. You would put subjective experience over God's word. You would console instead of encourage.