His 3rd game was played behind an offensive line missing 2 starters, but regardless, it's way too early to know exactly what to expect from Conner. Those of us who've watched him for a long time, back to his Pitt days, know what kind of pure talent he has though. While he's not as purely talented as Bell (especially in the passing game) he's no slouch and more than good enough to keep the Steelers' offense clicking. Him and Bell together would've been one helluva 1-2 punch.
It'd be foolish for anyone to try and justify how the Steelers offense is as good or better with Conner. That's crazy talk because it's not. It's a much easier case to make that the Steelers don't miss Bell a whole lot though... some, but not a ton because of the level of talent they have everywhere else. They'll score a lot of points whether Bell comes back or not.... and I think it's 50/50 at best on if he plays another down for the Steelers.