I used to train kata religously. Everyday, working the patterns of Moo Duk Kwan.
I havent done a form in over ten years now. There are some merits to kata, such as muscle memory, and the perfection of techniques,but it lacks much to be considered a "Complete" training regimen.
First and most importantly, kata lacks resistance in its training. Everyone performs better when there is no pressure. Simply because you do it well in the air doesnt mean that it will be so in self defense and that can be dangerous.
Secondly, Kata developes pattern. Order and pattern has no place in the chaos that is battle. The best fighter is a mystery undefinable by his opponent. You cannot stop what you cannot anticipate. You cant expect the outcome to be good if your reaction to a given situation is the same everytime. As a fighter, if I know what you are doing or going to do, you will not do it without being punished for it.
Third, I would suggest that most traditional systems are too expansive, Encompassing too many techniques. You dont need 500 techniques. In fact you probably would do better with less than 100. As for striking, I utilize around fifteen techniques regularly. Even with so few a number, there are virtually endless variations to techniques and combos. Reaction time is key to defense and you simply dont react as fast if you have too many options to weigh.
"When I let Go of who I am, I become who I might be."