No tourist will be going to downtown Orlando so that journey stat is basically irrelevant. 20 extra minutes in this context does make a longish transfer after a long-haul flight even worse. If they were moving from International you could make the argument the speed to get through Melbourne would offset that. But they’re not, they’re moving from Sanford where TUI more or less has the monopoly on international arrivals anyway so immigration time will be no different. That was one benefit of Sanford over International, much further by road but much quicker to pass through.
This will be very much advantage BA/VS along with anyone new entrants that might come onto the route.