In terms of how some/many measure success, a strong opening weekend is obviously crucial. But to this threads question, I think SRs fair-to-middling opening says less about SR and more about the baggage that the character carries.
SRs marketing was adequate, it opened very wide and had favorable/positive reviews. All the ingredients were there apparently. Yet, as you say, it earned (only) a respectable but not impressive $53M. Forget about SR being crap or having bad word-of-mouth or getting swamped by Pirates 2. Thats relevant with respect to the 2nd, 3rd and 4th weekend but not the 1st. In comparison, Iron Man (who?) made $99M. Why the discrepancy? is the question.
On its opening weekend, MOS is going to have to convince people that its something new/different.