If you are just measuring walking distance, yes it would be less. Assuming a similar walk in from the parking lot to either Epcot or DHS I would guess the walking distance difference would be about 2500 feet.
It would take a lot longer on the boat. You would have to stand and wait for the boat which could take 0-20 minutes. Then the boat stops at Swan/Dolphin, YC/BC, Boardwalk, and then World Showcase. The walk from the boat dock to the International Gateway is fairly short. Certainly shorter than the walk in from the front of Epcot. It has been a while since I have taken the complete boat loop but I recall thinking about how slow it was.