Lefty is not the reason why the Steelers lost. Not a great game, but not the reason Steelers lost. Defense played their butt off, special teams forgot to show up. Some would say Haley had a bad game, couple questionable calls, but overall, the dagger was the punt return. without that, Steelers win 10-6.
I do however, think Lefty was playing injured and that hindered him a little bit. Clean up special teams and the turnovers and bring the same effort to Cleveland, Steelers win no problem.