No, that wasn't the worst loss. That was the opening game of a team coming off of a 5-11 season against a Browns team that eventually won the division. A Steeler team that turned it around after it's first two horrible beat downs and made the playoffs when there were only 5 AFC playoff spots to take at that time (Three division champs and two wildcards. They added a third wildcard the following year.)
No, to me, these are the worst Cleveland losses:
Pittsburgh Steelers 6 at Cleveland Browns 13 Thursday, December 10, 2009
Pittsburgh Steelers 14 at Cleveland Browns 20 Sunday, November 25, 2012
Two much more recent games under the same coach, both coming off of playoff years, one a super bowl year, and both losing to bad, bad, bad Browns teams. This past Sunday's loss was more of an indication of where both teams are headed.