There's two parts to an NFL player's game - physical and mental.
Physical things can be coached up, like better strength, learning footwork, hand placement and so forth.
Mental things for the most part have been learned in Pee Wee football, high school and college, or they're not learned at all.
I'll give him a pass this year, after all he is a rookie, just getting used to the speed of the NFL game is a common thing. Maybe he's just gotten in some bad habits trying to handle top pass rushers, etc., and will improve in the next year or two.
But Mazi is not just not getting better, he's declining. For a guy who was supposedly stronger than the usual DT, he gets pushed around/stalemated far too often. And he's in his second year.
I'm sure Guyton and Mazi will both be here next year; we'll see what happens...