The MC is made a warrior because of them doing well in a battle or something honorable while others are done via assessment.

* Depends on your story. Becoming a warrior should mostly be an important moment in a character's life, and thus punctuated with an important reason. If anything, assessments are kinda boring. They're just cat tests with nothing that remarkable about them. Of course, give some attention to the other apprentices - have them defend the Clan, tirelessly rebuild the camp after disaster, something.
OR you can make assessments actually interesting and more than just "hunt prey real good." Let RiverClan cats be tested on their swimming skills, such as speed, grace, and treading water. Have WindClan cats be tested for their endurance in races around the territory, tested on their form and focus while also being aware of their surroundings. We know how cats hunt, we don't need 50 assessments on that!