It's certainly a tricky question, given the wide appeal of these properties. On the one hand, putting them behind a Disney subscription wall would be a huge encouragement to subscribe. On the other hand, you can imagine that there are lots of people who like these films but wouldn't feel like a Disney streaming package is for them, and would just turn to lots of the other good content out there.
The wide release Star Wars/Lucas and Marvel movies are designed to be seen by everyone -- which means their PG-13 take is too infantile for some, and too mature for young kids (IMHO, though I do see 7 year olds at violent films like The Dark Knight). In other words, their content, production budget, advertising budget, and distribution method are all linked.
But those pieces are all linked for original streaming content as well, which is how you can get something mature like Jessica Jones to be effective and valuable on Netflix.
So rather than choose between putting every Marvel property they can in wide distribution vs. putting every marble property they can behind their own subscription wall, what if Disney developed new Marvel series and films that connected more to Disney's family-friendly brand? There is a whole new young generation of X-Men characters who are kids and teenagers, and the dynamic of hiding mutant powers and feeling out of place because of them translates perfectly to the idea of a series centered around child mutants who live at home and go to school.
Marvel had long time imprints called First Comics and Epic Comics which were allowed to arrange more widely from the mainstream Marvel Universe; First was particularly targeted towards younger readers. There's a ton of audience-tested characters and storylines that can be mined.
Similarly with Star Wars, there's plenty of room to build programming in the Clone Wars vein that has a somewhat different audience than the wide release movies.
As for ESPN, I think the appeal of ESPN as a bundle could be enhanced by similarly focusing on content that appeals especially to ESPN viewers. For instance, where can I go right now to watch all the Fast and Furious movies? I have Netflix and Amazon prime and Sling TV, but I have no idea… I assume I could pay to rent them on Amazon. What if ESPN licensed this kind of content long-term?
The crazy thing is that I don't think it would even need to be an exclusive license. One of the downsides to the sprawling complexity of offerings by Netflix and Amazon is that it's so hard to know where to go to watch a particular film. If ESPN expanded their brand to be "all the action and sports movies you ever want to watch", the bundle economics might make sense of outbidding Netflix and Amazon on these properties.