The Bengals have had two extended runs of success -- the 1981-1991 and 2010-2016.
What ended both of them -- going cheap on the offensive line and letting guys go in free agency.
The Kenny Anderson (who should be in the HOF)/Boomer Esiason Bengals of the 80s fell apart when they got cheap and lost Max Montoya to plan B free agency. After that, the team stopped winning.
The 2010s Bengals had a great team -- until they let left tackle Whitmore and Guard Zeitler leave in free agency because they didn't want to pay them so that they could pay the D-line and a fragile AJ Green.
As many teams before discovered, no QB is good when knocked on their butt all the time and they went from 5 straight playoff appearances to dreadful in short order. The tackle helped the Rams get to the super bowl. The Bengals whiffed on several drafts of replacing those guys on the offensive line and have been bad for 5 years because of it.
It does start in the trenches, but if you cannot protect your QB, they get hit a lot, they get squirrely feet and innaccurate throws,, and they get hurt (see Dak last year, the same Andy Dalton behind the bad lines of the Bengals, the Bears QBs, Darnold with the Jets).