I guess "Mechanistic understanding" was meant to contrast against machine learning, not quantum mechanics. To elaborate, machine learning means fitting of a bunch of data by a given model. In science (eg lattice QCD) one often tries to theoretically (or computationally) explore regimes where data is not yet available. As a (former?) theoretical physicist, I am more than happy to admit that this is not immediately useful, though it will hopefully become useful in the long run.