This thread started out asking what makes Panther the largest company. Essentially, was it fleet size or revenues. It doesn't matter whether Panther or FedEx Custom Critical is the largest, or that they carry freight that started out as general freight. Each company, in it's own right, is structured as an expedite carrier.
FedEx Custom Critical is a stand-alone operating company within the FedEx corporate stable of companies. They often "rescue" freight from other FedEx carriers and from other LTL carriers and expedite the freight to its destination. Panther does identical work, even occasionally, from FedEx carriers.
Given the cyclical nature of expedite freight opportunities, and the constant flow of O/O's looking for greener pastures, all successful expedite carriers adjust fleet sizes throughout the year. Since these two carriers are nearly comparable in fleet size, a census at any given moment could show either carrier as having the largest fleet.
Personally, I don't care how many trucks are in the FedEx Custom Critical Fleet, nor do I care about the daily run count. My only concern is my monthly run count. I have a symbiotic relationship with the carrier; I provide excellent service and it reflects on them, and that gets them more run opportunities which helps me.