Whatever. You need your own appraiser, ordered and paid by you. There are only you and the appraiser, no developer and no subcontractor. None of it helps ...
Let the other one come first. Prohibit everyone present from making any changes to the installation. Announce that you will bring in your own expert afterwards. The general contractor’s expert cannot rewrite the standards, the functional defects are present, and he himself may also have a reputation to lose.