Agree it is difficult for fans. You almost have to know where the runner will be at an approx time and allow lots of time to get around.
Better to just go somewhere and stay put. The car traffic coming and going into the marathon is bad. Taking a bus works well. Or at least has for us.
This year I purely lucked out going in. Otherwise it was quite a traffic clog around Epcot and MK.
I think fans have to have a well thought plan, be lucky and/or persistent.
We stayed at WL and really enjoyed it. (2 adults) But it was not marathon time. (August)
Even at the AS and CSR we never experienced a traffic problem. DH took the special marathon busses. I took the resort busses. MUCH less probem than trying to get in and out by car during the marathon time.
I asked DH his opinion on the Ideal WDW resort during marathon time. He said WL is a No.
The monorail resorts, guests may gain some. He added he has spoken to runners who have stayed on the monorail resorts thinking they may have an advantage.
What ended up was the monorails were packed, with long lines. And guests have to switch monorails to get to Epcot, which was just another long line ending with another crowded ride.
At least with busses, Disney will have them lined and ready to go, one right after another. Anyone riding a monorail knows they stop just to leave a set amount of space in between. They will have more monorails in service. But only so many, no matter what. And it will not be one after another, like the busses.
His thought on the AS, Pop, CSR, is that MANY runners stay at these resorts. Especially at CSR, the Leukemia Society puts up their runners there. Due to this he thinks their marathon bus service is better prepared and more effective.
Even at cheap-o ASMu, the ONLY issue we ran across was that around 1:00 a.m. marathon morning Bus Loads of Cheerleaders were leaving.

And they were all over the parking lot and resort doing what they do best. Nuff said.

Luckily we both always had a hard time sleeping the pre marathon night anyway. He was always on marathon andreline. Me Disney andreline.