They are an imperfect approximation of an ideal truth finding endeavour implemented by imperfect humans. That doesn't mean that the imperfections are a feature, it means that as time goes on society should work towards making more accurate approximations of this truth finding process.
Just as we have done away with things like expert testimony on phrenology, cruentation, or trial by ordeal there may come a time when we do away with witness testimony or restrict the kinds of things we allow witnesses to testify about, like we already do with hearsay.
They are an imperfect approximation of an ideal truth finding endeavour implemented by imperfect humans. That doesn't mean that the imperfections are a feature, it means that as time goes on society should work towards making more accurate approximations of this truth finding process.
Just as we have done away with things like expert testimony on phrenology, cruentation, or trial by ordeal there may come a time when we do away with witness testimony or restrict the kinds of things we allow witnesses to testify about, like we already do with hearsay.