I don't think that business logic applies to tourism. As long as the number of tourists is increasing and everyone is making more money everyone is winning. I live in Vegas and if someone builds a new $5 Billion hotel next door and we end up getting a 10% boost in revenue without spending a dime I guarantee our CEO and shareholders don't care what the new hotel made.
See, that's what a difference ten years makes. MagicYourWay changed that game.
Every move Disney has made in the last ten years has been aimed at getting folks to see WDW as a one-stop destination. You go to the website, they make it sound like you pretty much need to stay on property. They don't even want you renting a car anymore. They want to collect you at the airport, bring you to the resort, drop you off at the lobby, keep you on Disney property your entire stay, pick you up a week later, and deliver you back to the airport.
The pricing system, the "free" DME service, the "stay longer" and "flashback" (or whatever they call it? something 'back') deals, and now all the MM+ stuff. - it's all about keeping you solely at Disney. They spent $2B on a system that largely is directed just to people who stay on property.
It's not like Vegas, or even the "old" days at WDW around the turn of the century. Back then, pretty much everyone rented a car, staying on site was a splurge not a near requirement, no one spent 6 or 7 days in the parks (they didn't even sell more than 5-day park hoppers). You spent 3-4 days at Disney, 1-2 days at other parks, and a day hanging out (back when Disney used to offer copious "activities" around the resort to entice you to spend money on that day).
But those days are long, long over. Because of how the pricing is stacked, and the large percentage of guests staying on-site, people spend their entire time at WDW. It's such an expense and hassle to do Universal as well, especially now since it's not a 1-day 1-park thing. Logistically if you don't have a car it's very expensive (or slow, I know a few folks who have attempted the public bus route). And when the price difference between 5 and 7 days isn't that much, most people just get length-of-stay, further discouraging "wasting" days and paying more when you are already getting extra Disney days cheap.
It's the reverse for Universal because of this pricing, too. If you are going to Orlando, and doing Universal, you really need at least 2 if not 3 days now. When you price that out, and then you start to look at spending a few days at Disney - it just doesn't add up. You realize that for the price of 3 or 4 days at Disney you might as well do a week there. They don't even bother setting foot on Disney property, unless it's to grab a bite at DTD.
That's why most folks are doing one or the other. Since there are so many other things to do in Orlando, you can easily fill up a week with Universal and Sea World and a few other things - or you know, just relaxing a bit (which people often complain doesn't happen when you are at Disney 7-days straight).
Anecdotally, I get at least 1-2 people a week contacting me asking for help or advice about an Orlando trip. In the past few years since Potter, and Disney's large price increases, the most that are inexperienced enough to ask me are going for Universal. These are the "new bodies" that are being brought into Orlando, not folks already on the pixie dust who couldn't imagine going and not doing WDW. Not a single one who is going for Universal does both. Some definitely think about it, but when they are looking at a $2,500 vacation just doing Universal and other stuff, and a $4,000 vacation doing just Disney, and depending on how it works out nearly as much to do both - they pick Universal.
Again, that's anecdotally, I completely admit - but what other folks say, and the logic of it - I don't think it's "good for everyone" because Disney has so insulated itself to increase profits that they now don't benefit from the "trickle down" anywhere near what it would have been like even 10 years ago.