Bluecher was IMO not a bad design per se, but it was a design based upon faulty criteria. In the North Sea, Bluecher was a floating liability; I do not consider it a coincidence that she was lost in her first encounter with British battlecruisers. Her optimal theater for employment would have been the Baltic where, provided that she managed to avoid entanglement with the few and conservatively operated but relatively fast dreadnoughts of the Russian Baltic Fleet, she could have provided useful service.
Had Bluecher been part of von Spee's Asiatic Squadron in place of one of the existing armored cruisers, I don't believe that the ultimate outcome would likely have differed. Her best bet would have been to directly flee at top speed; although the battle was fought in generally excellent conditions, the weather actually closed down not long after the end of the battle and her speed advantage over von Spee's older armored cruisers might have afforded her a sporting chance to find refuge in the failing visibility.
Her inclusion in addition to Scharnhorst and Gneisenau would have placed a significant additional logistical burden (coal) upon von Spee. The potential operational consequences of that are difficult to objectively analyze. Tactically speaking, it certainly would have complicated Sturdee's task at the Falklands if all three German cruisers had stood against him, but the Germans still had no realistic hope of achieving victory. My guess is that any German cruiser fortunate enough to have survived the Falklands would have ultimately been interned or scuttled.
Re Bluecher's main battery rate of fire, the proving ground maximum mechanical rate of fire of any gun is not meaningful in analyzing practical warship rates of fire in battle. Under true action conditions, rate of fire is first and foremost governed by the engagement range (time of flight) and secondly by fire control and spotting considerations (time required within the fire control system to spot and transmit fall of shot observations, process the data and send corrections to the guns). Maximum mechanical rate for a turreted gun was not even achieved in rapid fire. The experience of SMS Derfflinger at Jutland being a good case in point. Her 30.5cm main battery gun was officially credited with a firing cycle of approximately 3rpm (20 second firing cycle), but according to von Hase, Derfflinger's demonstrated main battery rate of fire under rapid fire was actually only about half the "official" maximum rate of fire figure.