Swan Reserve is a little farther than Swan-Dolphin because it’s across the street. So I’d think of it as being maybe another 1/2 mile or so walk further… kinda depends on where you measure from, or iF you find a shortcut across the property. I’m talking realistic distance from say, the lobby.
To make up the walking distance, you can always take the little boats that travel the lagoon. They pick up right behind the Dolphin, and on the other side of the bridge at a couple points around the boardwalk area. Taking the boat from the Swan-Dolphin load point would more than make up the extra distance to the Reserve.
The boats are fully able to accommodate mobility devices such as wheelchairs or scooters, also— just in case that is a concern.
We stayed at Dolphin last year, and it was
super convenient for getting to Epcot. We basically used Epcot as our “jumping off point” for the rest of the resort. We were only there for 4 of our 10 days, but wow, was it awesome. For the price, we were a little disappointed with the room itself being kinda run down & dated. The newer Reserve would certainly be nicer in that regard. It was also very cluttered considering it was an accessible room. We had to push quite a bit of unnecessary furniture out of the way.
[They seriously need to get someone in a wheelchair up there to show them why a coffee table and a dining table plus a couch and multiple chairs— 3 armless and 1 armchair— is just way, way more furniture than needed and actually makes the room less accessible.]
I can’t speak about the pool or other amenities at the Reserve, specifically . The pool we used at Swan-Dolphin was pleasant. It wasn’t anything super special, but it was clean and had plenty of chairs. The water was cool for what we were told was a heated pool, but it wasn’t bad— just a bit of an “Oh-ooh” feeling as we got in (if that makes sense?) Once we were in up to our torso, it was fine. I know there were at least 2 pools to choose from and iirc we picked the adult or quiet pool.
I would think the pool at Reserve would be pretty nice since it’s newer. Not sure if they have multiple pools, but they probably do. I vaguely recall them saying that we could use the pools over there, we just didn’t.
I’ll try to find a map or overhead image to illustrate, but if it were me, and being close to Epcot was my primary consideration for choosing a resort… I would go ahead and book at Reserve.
Overall, we were quite happy with the resort.
Hope that helps. 
