It was somewhat of a mistype on my end, but in general, second hand accounts have said that he was not happy with the way the rest of the world infringed upon his vision. He wasn't unhappy with DL, he was unhappy with the overall package of DL and the lack of immersion due to the rising and expanding city around it.
And quite frankly, that's one of the reasons I won't go back to DL - I don't like walking outside of the park gates and feeling like I'm back in the "real world".
He was also reported as having said that WDW was indeed his true vision (Progress City and EPCOT included) in the way that it was to be a fully immersive and "life changing" experience. The utilidoors were one of his ways of creating that sense of immersion (even though reports say the company would never incorporate such a thing ever again).
I really want to find the info I have. I'll have to look around the house for it. You learn a lot of this stuff on the Keys to the Kingdom tour, but you also learn a lot by asking the people who are in charge of that tour. Stuff they don't teach/explain to you normally, haha.
E: Also, the fast pass system is in place for a VERY good reason. Yes, you have to make a tough decision regarding which of the "tiered rides" you want to use a fast pass on, but when you read and hear about people who abuse the DL fast pass system...It makes sense. Also, when my wife and I go to WDW, we never wait more than 45-60 minutes for the "top tier" rides that we didn't use a fast pass for. We don't like Soarin', though...We waited 4 hours for it when it first opened and have hated it ever since, ha.
I've had a personal conversation with an Imagineer on the planning and implementation of the fast pass system and the incorporation of the Magic Bands and how they intend to further their functionality and ease of use. It's a super fascinating system that is, quite frankly, way more advanced and refined than people seem to think. And as someone who deals with infrastructure and logistics on a day to day basis, Walt and his crew were decades ahead of their time. It's crazy when you really sit down to think about it.
E2: I need to reiterate that this is ALL subjective and second/third hand information. I am not looking to piss anyone off or come off as confrontational. It's Disney - any Disney is good Disney.