I've done all variations of transportation on previous Orlando trips; DME to and from WDW, strictly rental car, rental there with DME back, and so on. In my opinion DME was mostly used because it was free (or at least built into the price). On trips to Universal, I never used their Superstar Shuttle or whatever it's called, because there's no true cost benefit.
If I'm going to pay for a ride from MCO to a resort, there's two things I will look for in the service:
1. Am I the only party in the vehicle? When I get off my plane, I want to get the trip started. I don't want to wait for a handful of other families to drag their children through the terminal and arrive at a mini-bus.
2. Can I stop somewhere to pick up supplies? With Mears, I've almost always used their one stop option. It costs about $5, and it allows me to stop at a Walmart/Publix/etc. where I can load up the car with water, snacks, beer, or whatever other essentials I want in my room. Haven't tried that with Uber, but I'm sure I could always slip them some extra money to make a quick stop, or just book two trips, MCO -> Walmart --> Hotel.
A pay-for version of DME or a train to Disney Springs will offer neither of those perks, and for that reason, I'll probably never use the service.
Between this and the restructuring of EMH, the only true perk I see in staying on-property is the early FP+ booking window. Upsetting to see..