The problem is that some of the hiddens get truly revealed so late in the game that you might have decent, very skilled fighter that will never reach the top. But as it takes so long to build them that you might be reluctant to cut them as you are already emotianaly invested too. It really sucks. I have couple ln my roster now. I know I need to cut them but I just cant..
Granite chin without ko power is still something you can work with. But Granite chin and low Heart and you are fooked. That is that your fighter will likely fold under pressure in big fights. If you build your fighter accordingly he likely has decent skills to cut thru lower levels in competition but as skilled fighters emerge with good hiddens, he is done.
So perhaps my advice is to release your fighter as soon as you can see that he cant be truly elite. What happens if he isnt the better skilled fighter in fight? What if you try higher damage etc. Once you know what your fighter truly is then you can also build your tactics around that.