Heyo!

It's not wrong to invest towards your ninjutsu more than attack, since nowadays many of the ninjas are mostly based on their ninjutsu. Nope, it won't be ''damaged'' and many of the ninjas, including the mains have mixed damage as well. If you decide for example to use lightning main, you won't have any issues with it. The same goes with the other ninjas that may have mixed damage. So do not worry!

Hope that helps!