I can't see any major issue in what FedEx Crew performed. Only thing is, they should've called out "going around" first, then maybe suggest Southwest to react like stop. Why FedEx went around so late? Well, we can't judge. This is very dynamic, they might have thought it works out at first. Even after the assumed major delay due to SW runup test.
I can imagine a sort of "non-constructive" role of the SW crew in happily accept the jump in front of the arriving traffic and doing whatever served themselves. Hope they learn from it, if that's the case. Hope it's not systemic to get advantage at sb elses' expense.
I can see a major screw from ATC, and to be honest, the conditional landing clearance was not the major issue. FedEx would have continued the approach almost as long waiting for the clearance. The major screwup is to let come a/c as close each other in poor vis conditions. And risking ILS signal quality by interference. I guess also a systemic one if executed by the same controller.
BTW, how often is low vis in Austin?