Most UPS people don't understand the FedEx business model(s). As illogical as it seems from your perspective, there are reasons the divisions are not consolidated. Both Ground and Home Delivery are independent contractors, so they cannot deliver Express pkgs, which are handled by company employees. Look at all the lawsuits over the issue of contractors vs, employees and you'll see why Fred can't have Ground and Home people doing anything but their own freight. Express has always been it's own animal, so to speak.
Ground and Home move exclusively via truck and rail, while Express moves mainly via air. The systems are not complementary, although that may change based on the outcome of the contractor lawsuits, the EFCA, and the RLA exemption.
It doesn't make sense operationally, but it does legally for now.