D+ was originally going to be a boutique streamer serving mostly Disney family fare. Then it blew past its five year subscriber target in a month.
Then came The Great Pivot. The confluence of:
1. buying Fox (which gave D+ a third of Hulu)
2. buying out the rest of Hulu from Comcast, and,
3. the rapid increase in 'cord cutting"
brought about the opportunity to make D+ merge together with Hulu to make a "four quadrant" streamer with "general audience content" (that is, adult fare, such as R rated content).
Disney's streaming went from "here's a repository of Disney family movies and TV shows" to "we're going to try to win the Great Streaming Wars."
So, in an alternate world without Hulu and Fox, D+ would have been a small, niche streamer and could probably make a small profit. Or it would have had to invent a walled-off "general audience" section of D+ for more adult content. But with Hulu falling into their lap, they didn't have to go that route.
Much of the current content that's popular on Hulu would have then been incorporated into D+ anyway. And then, Hulu wouldn't have been that popular with just Comcast content.
Just like Star Wars or Pixar "is Disney," so, too, "Hulu is Disney." The merger of D+ and Hulu was in process for the past 4 years. It's one streaming service with a bundle of brands.