I’ve noticed this too. Sometimes we get early check-ins. It is only in recent years that we’ve had late check-ins.
I am not convinced the wording ‘starts’ at 4pm was intended to imply WDW/DVC has the right to give you a room anytime that evening. My interpretation is check-in starts at 4pm so never rely on getting an early check-in. But legally the contract is 4pm check-in and 11am check-out. That is the terms. If they don’t deliver your room until 6, 7 or 8pm… they are NOT protected by that ‘starts’ at 4pm wording. There’s reasonable grounds to request a partial credit and if that fails, escalate via payment source of credit card. Now we can choose to be gracious and accept late check-ins, which so far we’ve done because in the big picture we’ve gotten plenty of early check-ins. But that’s not the same as meaning I must accept all 7pm check-ins. If 6pm check-ins became habit on their end I would start pushing back anytime it inconvenienced our plans.