Suggesting a change like this is hard, you have to see how the ship will behave according to other PCAs.
Gun size is not the only important thing in the game... you also have to consider speed, AA platform, spread, ship size, playstyle... there are many different factors that come into play when you define a "good ship".
If you put bigger guns on the Moltke, how do you think it will play against other ships?... consider its already an amazing AA ship and very fast. You also have to think that maybe the changes to make PCAs even don't come in the Moltke... maybe you need to rise the speed or improve the spread of other ships... maybe it's not the Moltke that is wrong, but other PCAs.
Focusing on just one ship and suggesting changes to it is never good... you loose the big picture.
Watch all ships, play all ships and then focus on what you want the big picture to be... then you will figure out what changes you need to suggest.