While the Skua wasn't a great aircraft, it was a competent dive bomber (ask the crew of the Königsberg about how useless it was). Unlike the SBD, it was operating in a comparatively target-poor environment (the Kriegsmarine was both smaller and its surface fleet less aggressive than the IJN) and in one where it was more likely to meet heavy fighter opposition. Overall, it doesn't compare too badly to the SBD.
The Roc was a piece of crap. Period. First, to be an effective fighter it must be reasonably able to combat enemy fighter aircraft; the Roc could not compete with biplane fighters in service at the time. Indeed, the Roc was barely faster than the Douglas B-18 or the Martin B-10, both obsolescent at the start of WW2. If the only thing providing air cover for your carrier task force is Blackburn Rocs, an attacking air group need not bother with escorts. The laden bombers (say SM.79s) would be faster than the defending fighters.
Could an effective carrier fighter be based on the Perseus engine? Possibly. It would have to be very carefully designed and would be more like the Curtiss CW-21/CW-21B or Caudron CR.714 than any really successful fighter aircraft.
The Roc was a very competent divebomber, and would have made a good recon and shore based short range strike aircraft, especially when fitted with a slipper aux fuel tank. Certainly the idea was flawed, but it could have been used to good effect in secondary roles. The Roc and the Skua were never meant to compete with single seat fighters.