Johnson didn't prop up anything - he cleaned house. Shelton, Jenkins, and Davis from last year's starting OL are all gone. He completely rebuilt a new one, and it's definitely not average. 3rd in pass blocking (86.8 efficiency), 4th in run blocking. Ranked 2nd overall by PFF in December. The interior is elite with Thuney and Dalman.
Ben Johnson was spoiled last year with an all-world veteran center, Decker mostly still playing at a high level, Sewell, solid guards, and depth. With so much talent, athleticism, and especially experience, he could run just about any play he wanted. And it would usually work.
He knew he'd have to recreate something similar in Chicago for his offense to work, so he did