True.....everything but Epcot. Those long inclines/hills at Epcot definitely take you by surprise, even if you've walked daily to build up resistance. Vegas is flat by comparison, and yes, been there, walked that, and the distances are definitely comparable.
I go to vegas a lot. Flights are $50. and I'm a bally's member so rooms are $50-$75. Its very affordable. But yeah, we do a ton of walking in vegas. Miracle mile, casino to casino, fremont street. I could go to vegas a dozen times and it still doesn't equal the cost of one wdw trip. But I'm not complaining!
Vegas would be a good prep location - particularly with the heat. As much walking as I do to prep, I can't bring myself to prep in the midst of heat and humidity. And, I certainly don't practice the quick poncho throw-on followed by running through rainstorms. Maybe I should??
I'm active all day but I increase my walking and number of steps the day after I book my trip. Gives me the incentive to stick with it. Those early morning to late night Disney days can really add up the steps. Youve got to do it long term to build the stamina. And start breaking in the footwear that youll be using so they are comfortable and you are used to them. A good pair of cushioned inserts are well worth using as well.