I mean, they weren't necessarily "bad" ships - they just came far too late for their intended role (countering German raiders in the Atlantic or Japanese "super cruisers" thought to be under construction in 1941). In service, the CBs were "satisfactory" (like all the large surface combatants), but they were too specialized to continue in service post-war. The guns and their associated shells were too expensive, the fuel cost was too high, and moreover there were only two CBs (Alaska and Guam) vs. four BB-61 class ships that could be kept in service. The four BB-61s had interchangeable guns and shells which meant a larger stockpile was available on hand vs. the 12" shells for the CBs.
As for the term "mini Iowas", well that's just nonsense and I'm curious where you heard it or if you just invented it yourself.
There were plans to resolve the issue of the large tactical diameter at the next refit (by installing two rudders vs. one), but the ships immediately went into reserve and the work was never carried out. In service, the two CBs primarily escorted carriers in the western Pacific in 1945, and they participated in shore bombardment at Okinawa, where, again, their performance was "satisfactory". By that point in the war the USN was in need of fast carrier escorts that mounted the 5"/38-caliber gun with attendant Mk.37 director - this was a deadly combination that was used to full effect during the kamikaze attacks on the fleet off Okinawa.
The 12"/50 Mark 8 gun was a very good gun system with a lot of hitting power - rivalling the 14" guns on the old battleships. It was just an expensive gun to produce.
In short I wouldn't call them "bad" ships... just ships that were too late to the fight.