Walrus said:
if you choose one theory over another
You are misdescribing what physicists are actually doing.
The prediction of classical General Relativity is that a black hole cannot lose mass. (That, btw, is the prediction that changes when Hawking radiation is taken into account. So your first misdescription is of the actual prediction that changes.)
Hawking and others have developed models that take quantum effects into account at least to some extent, and those models generally predict that black holes should emit radiation, which, if nothing else ever fell into them, would cause them to lose mass and eventually evaporate away. However, these models are only provisional because we do not have a good theory of quantum gravity.
So it is not a matter of "choosing one theory over another", it is a matter of not
having a theory at all that takes into account all possibly relevant effects. But in practical terms, this is not an issue at all, because, first, the estimated Hawking evaporation time for black holes of stellar mass or larger is many, many orders of magnitude greater than the age of the unvierse, and second, all real black holes do have things falling into them--CMB radiation, if nothing else--which adds mass to them that swamps any predicted mass loss due to Hawking radiation.
Walrus said:
nothing escaped the event horizon of the black hole which could not be seen, but now we see them.
This is still another misdescription. We do not "see" black holes because of anything escaping from inside their horizons. We "see" them because of their effects on nearby objects and radiation
outside their horizons.