However Fed Ex is willing to lose money on contracts just to get more volume, UPS will not.
Both companies are very similar here, obviously no one wants to lose money on a contract, but it can happen and to either carrier. UPS can undercut Fedex and vice versa for a job. How aggressive one carrier is at some point in time, depends on how hungry they are, that can be nationwide, regional or local in focus, many factors play into the strategy. But I wouldn't believe Fedex is more willing to take a job to lose money (it can happen) than UPS. Both companies are extremely competitive with one another. Assume most of the time when there is a switch in carrier that the other came in with a better rate, as you know both carriers take business from the other, #1 reason rates. Why? Because the #1 reason for the buyers is reducing cost. Pretty simple, pretty darn common.
Or here look at it this way, one has to think Amazon is all about cost, they'll use USPS, they'll use regionals for Pete's sake. So you didn't have the majority of business because you were Cadillac's to them, no you had the best overall price and for a good while, better than Fedex. So who was low-balling who with the single biggest shipper?