Integrity

Tai chi classes that study the art martially need not train in a uniform manner.
They may never have anything like the martial credibility of judo, karate etc... but it is possible to train the martial art with integrity.

Trained properly, tai chi should offer all the same skills as any martial art.
And a lot more besides.
To accomplish this you need a comprehensive understanding of what 'internal' actually means.
It is necessary to recognise the differences between combat stances, strength training stances and performance stances.
Your art must be tailored to function martially.