The cost still matters because if the losses cost less to replace than the superconducting material costs to install, no one will use it. So parents point still stands. It doesn't matter how high the electrical efficiency is, what matters is cost efficiency.
This is only true to a point. Evaluating incremental cost benefits on the basis of the delta of energy loss along specific lines ignores the state change that occurs when main trunk elements of the grid become lossless and energy generation and storage solutions can be deployed in a near-location agnostic manner.
As with all toy models being applied to the real world, there are important factors to model in that aren't immediately obvious.
