British capital-ship depth in an earlier Rheinübung

Would an earlier Operation Rheinübung have left Hood alone against Bismarck?

No; Britain had additional capital ships available beyond the first ships assigned to the interception.

The initial list of ships did not represent the Royal Navy's entire available depth. Secondary and tertiary capital ships, including Renown, could be called into the hunt if the first interception failed or the main battle force suffered damage. The later concentration against Bismarck demonstrates how quickly additional units could be drawn into the operation. The forces immediately assigned to an interception were only part of the reserve a global navy could mobilize as the chase developed.