You said that philosophy is only limited by the need to be internally consistent.
Well, for one, religious philosophy is often not internally consistent. Same for eastern philosophy. And most of the history of western philosophy, for that matter. So even your one criterion doesn't work when you force it to be universally applied to everything that's ever been given the title of philosophy.
And that's the problem with your statement. It takes the broadest possible subject in the history of man and makes a generalization about it that at best applies to some small sub-set and at worst applies to absolutely nothing.
What you are talking about is the validity of a philosophical argument. But just about every discipline in philosophy is also concerned with the soundness of the argument.
Even things like ontology or metaphysics are concerned with correlating their arguments with the way things actually are in the world.
Otherwise, all philosophical discourse would occur in symbols. But instead, the factual accuracy of the argument's constituent premises is also important.
So epistemology, ethics, political philosophy, aesthetics, philosophy of law, religion, mathematics, and language... 100% of these things are concerned with much more than being internally consistent.