I don't think Bell is as big a factor as he's made out to be. The Ravens success against the Steelers comes from the fact the team has been built to beat the Steelers, as well as the Patriots. Won't always happen, but the pieces were put in place for those two teams.
The team is 6-3 against the Steelers since Bell was drafted. Keep in mind the horrible 2015 team that swept them and the 2014 playoff team that beat them with CBs not even good enough for the bargain bin (minus Webb I guess).
in the four seasons before Bell, Baltimore was 5-4 against the Steelers. So Baltimore was still pretty successful against the Steelers.
Pittsburgh has become too reliant on Bell, and that's what will stop them from truly outplaying the Ravens. RBs are rarely the x factor against Baltimore, no matter who it is. There are exceptions, but Bell clearly isn't one of them, not for the Ravens.