Each Person Is Entitled to the Derech That Suits Him
We end the Torah with the uniqueness of each Shevet. This teaches us that each person is entitled to the Derech that suits him. Yet, the same person should understand that he can't always stick to his Shita, and at times he can borrow Yesodos from others. This also promotes Achdus; when we realize there are opposite Shitos. And it is fitting that the Torah which was only given when there was Achdus (as it says: וַיִחַן שָׁם יִשְׂרָאֵל נֶגֶד הָהָר יתרו יט ב כְּאִישׁ אֶחָד בְּלֵב אֶחָד רש"י like one person with one heart) should end with this message.
When you realize that people are different, this prevents Kin'ah, and you don't have to imitate even great Tzaddikim.