Speaking as someone who is constantly pushing a wheelchair at Disney, get ready for a calves workout.
The only park where a wheelchair is a leisurely push is Hollywood Studios as the only area with inclines are attractions such as Star Tours, Smugglers Run, Rock n Roller Coaster, Midway Mania, and the Frozen show off the top of my head. Star Tours offers its own line for wheelchair users and detachable armrests in Cabin B to allow for an easier transfer, Runaway Railway has its own wheelchair loading area, Midway Mania has its own wheelchair vehicles.
Animal Kingdom is my personal nightmare as the Oasis is an explorable incline, Flight of Passage is a long and giant incline, there are inclines throughout the park which your normally don’t pay attention to, and of course the incline at the end of the day back into the Oasis. Kilimanjaro Safari has its own trucks that allows for a wheelchair to be rolled in, as does the train for Rafikis Planet Watch.
Magic Kingdom isn’t that bad unless you insist on using monorails to get to the TTC or the resorts are those inclines can be tedious. Magic Kingdom also has the dreaded trolley tracks which have led to many close calls with my dad nearly falling out. Small World, Pooh, Pirates, all have inclines and many other rides have a special wheelchair specific line to avoid stairs at this park. Jungle Cruise and Small World each have their boats where you can wheel in the wheelchair, with Small World having its own queue for wheelchair users. Mermaid and Pooh allows you to roll the wheelchair right into certain vehicles. Thunder Mountain has its own separate queue for wheelchair users as well.
Epcot has notable inclines to enter The Land all though a wheelchair lane is available so it’s not too bad, inclines in the pavilion aren’t too bad but are carpeted so makes wheelchairs a tad slower. The first portion of Nemo’s queue is inclined, Figment has an incline as well. The entrance for Mexico is an incline, and the worse incline in the park is the one between France and the UK. Many tires for the wheelchair have gone rogue here! Nemo has its own wheelchair vehicles. Living with the Land and Three Caballeros have their own wheelchair queue and wheelchair boats that can be rolled into. Spaceship Earth has its own wheelchair entrance.
All the special wheelchair queues are offered to you without needing a DAS as these queues either have stairs or are too narrow for wheelchairs to use (I guess, never debated with the cast members)