Wasting decades on String Theory? We've learned String Theory and Brane Theory both yield the same results as the Standard Model (QFT). Nowadays physicists use the model that makes the computations easiest for the problem at hand.

My own thoughts as a well-learned armchair physicist is GR is the wrong model and Einstein's field equations aren't the right model allowing us to include gravity in QFT. This is what most actual physicists believe, and for good reason. Of course it's entirely possible that QFT is also the wrong model and we need a completely different model from everything we have today in order to form a theory of everything. That's what String Theory and Brane Theory attempted to do. The problem being is thus far the new models don't predict any different results than does the existing model - they all appear to be equivalent. But you can't know that unless you tried, so it's not a waste of time.