FedEx Ground started as a different company (Roadway Package System) -- to this day, it has a lot of contracts, union rules, etc. which make it vastly worse than just a ground version of FedEx. The only FedEx acquisition which seems to be any good is Custom Critical (used for shipping organs, live animals, etc. on next-flight-out commercial service, to get stuff door to door as fast as possible).
Consider that despite billions in investments, both DHL before they went away and FedEx Ground today are still not as good as UPS.