You challenged me to do some research, so I did. And at your request, I wont include a single stat about sacks.
First, lets look at overall Pass Block Rating.
Pass Block Rate
Dolphins: 51.8
Bengals: 53.1
League Median: 67
So in the overall pass blocking stat, the Dolphins are worse - but BARELY. They are essentially the same and both well below the league median.
Pass Block Win Rate
Dolphins: 47%
Bengals: 49%
League Median: 61%
Run Block Win Rate
Dolphins: 71%
Bengals: 71%
League Median: 70%
Now (above) we look at how often each teams offensive line won their battle in both pass blocking and run blocking. They were identically tied for run block win rate and extremely close in pass block win rate.
Time To Throw
Dolphins: 2.5
Bengals: 2.68
Bucs: 2.5
Packers: 2.6
Now (above) we are looking at how much time the Dolphins gave Tua to throw. Average of 2.5 seconds. Which is the same time-to-throw that Brady had. And almost identical to Rodgers and Burrow, too.
Conclusion
Tua had the same amount of time to throw as Brady, and was within 0.1 seconds of Rodgers/Burrow too. He also had a run blocking line that was identical to Cinci and a pass block offensive line that lost only 2% more of its plays. By every non-sack stat I know of, the Bengals and Dolphins are extremely comparable and had essentially the same offensive line production last season.
Tl;Dr You can say that the Dolphins line was worse and I'll agree with you if you'd like. They probably were slightly worse. But it was not by much.