indeed , every jutsu has a weakness, but you can combine two jutsus that cover each other's weakness
example ?
Tsukuyomi : weakness : looking away :
amaterasu : weakness : looking in the eyes : (because if you look closely , you will know when the justu will form whn the eye bleeds )
so if he is able to use both perfectly : if the victim looks away to evade tsuk : he amaterasu's him , if he looks in the eye to check when the ama flame will come out : too bad that's tsukuyomi hitting him
another example
totsuka blade : weakness : no defense , but a deadly attack
yata mirror : weakness : no attack but best defense ever
combined : best atk and Def ever

no way out !