As far as why other tzaddikim disagreed, each tzadik’s source in the sefiros direct the way he serves Hashem. Fire example, Avraham Avinu personified chessed of atzilus, while Yitzchak did gevurah.
So tzaddikim can disagree because their neshama and Avodas Hashem can be rooted in different sefiros
There are twelve shvatim not just one. Ailu vailu divrei Elokim chaim.