We've been there a lot of times, pushing DD's wheelchair. Many (not all) of the paths are narrow compared to the other WDW parks. Many are themed so that the concrete simulates things like mud paths.
Most of the parks have at least some areas where the concrete simulates other things (like cobblestones in parts of Epcot's WS and in MK).
The pathes at AK are smoother than most city sidewalk systems (where you might run into cracked blocks or blocks that are raised compared to the next block).
The standard rental wheelchairs have a sling seat and back. What a lot of people do to make the ride more comfortable is bring a pillow or a chair seat cushion. Makes the seat much more comfortable to sit in.