its wrong to suggest that if you practise X, then you will only become good at X.
practise alot of external martial arts, and you will also become faster at running, better at jumping, better at basketball, better at lot of things.
the same is true of internal MA. simply doing TCQ forms wont just make you good at forms, it improves other stuff. Truly, health is improved, truly internal power is improved, truly whold body co-ordination, being able to listen to your body etc will improve.
i dont understand how this misguided idea came about, well i do... but even if i do something really basic like practising making cups of tea, it follows that i will also 'improve' my skill at making coffee, even though i dont actually do it. isnt this common sense?
every time we use our bodies we cannot do just one thing, we do many.
Ecce nunc patiemur philosphantem nobis asinum?
what transcends the buddha and the law? Cakes.
"Practice is better than Art, because your practice will suffice without art, while the art means nothing without practice." - Hanko Doebringer, 14th century