He is a functional guard right now that should continue to get better. He has been moved so much and has had some terrible coaching, last year was the first year he had a real coach since Notre Dame (even then the Notre Coach should have fixed the arm extension issue). He looked pretty solid at guard, he doesn't play center well.
Physical limitations, he has T-Rex arms and the way he uses them makes it worse.
He lets people into his body (which for two years with the Dolphins staff made worse due to the stupid Cable technique they were using), he lunges because his feet slow down, his feet need to be quicker due to that arm length. Because of these arms and feet his hand placement becomes more important. When he keeps his feet moving, his arms out and the defender out of his chest he actually not bad in fact pretty good.
That is a coachable and solvable problem, he has enough of the tools to be a decent if not good player on the line.