There are many types of Strength, spiritual, mental, physical. If you are the strongest you need to have both leadership skills, the intelligence to act smartly as a leader, and strength to fight, and Baki isn't as weak as you think. How are you so sure he's just a regular jounin, and also Konoha is supposed to be the strongest of the hidden villages, so the Hokage level might be higher then the Kazekage level, which means Baki has a chance to become Kazekage.