Let's not forget that back in the days of Walt, he had a lot less IPs under their corporate belt than they do today. If Walt had all the IPs that the corporation owns today, perhaps we would have seen a Disneyland that was almost entirely based on Disney IPs.
It's a theoretical question for sure, because AFAIK, there is no statement from Walt on the record about what a good mix of IPs v. non-IPs is. But he certainly was a master at appropriating public domain IPs for movies... and also for park attractions, like his use of Mark Twain and Tom Sawyer.
In a theme park, every ride has a story, otherwise, it'd just be a carnival ride. For rides where a Disney IP fit, it was IP'd. For rides that didn't have a Disney IP, a fitting public domain one was used (and then Disney got around later trying to make that IP into a movie with varying degrees of success). The number of rides with a truly generic story were not a lot. And as time went on under Walt, became fewer.
I agree with you both that an attraction has to be good in and of itself regardless of the IP. And an Disney IP overlay can't make a bad ride good. But, I'm not on board with you
@marni1971 that there needs to be something of "an appropriate mix" of IP v. non-IP. If the Disney IPs work, great, even if it upsets the 'mix.' Though, I think we both agree it shouldn't be 'forced' such that it's out of place or an attempt to make sub-par work palatable.