Nah, man, it's not about seniority or salary. Radakovich can fire Mario. Might cost money, might cost political capital, but Mario's 10-year contract doesn't give him carte blanche forever.
I'm not sure why people try to analyze every job at Hecht as if it is purely a hierarchal type of military command structure. Alonzo has a lot of power, even if it's not "I fill out your performance evaluation" power. If ****e goes south for another few years, and Alonzo recommends firing someone (HC and/or coordinators), I'd be willing to bet anyone that Radakovich will agree, contractual terms be damned.