I would agree, if it weren't for the fact that at DL/DCA, you don't have to go to the ride to get the return time, you get it from a kiosk.
Also, Disney has taken away the biggest incentive to cheat the system by eliminating the unlimited FP (or better) access that the GAC provided.
My understanding is that the 10 minutes off is to account for the time spent in the FP line; it has nothing to do with where you get the return time.
As I understand it, the reason DL has kiosks and WDW doesn't has to do mainly with 2 things.
1) WDW already has had greeters at each attraction for many years. So, they had CMs available at each attraction who could give out the
DAS Return Times.
To put kiosks for DAS at WDW would have meant adding additional CMs to staff the kiosks when they already had CMs who could do it.
WDW is larger than DL, so walks between kiosks would be farther.
2) DL did not have greeters at each attraction (at least from everything I know). To add a greeter for each attraction would be adding a lot of CMs, and in some cases, adding a CM at an area/entrance that is already tight.
Kiosks were chosen apparently because of efficiency - one CM could handle a number of attractions and since the parks are relatively small compared to WDW, the distance between the kiosks would not be that far.
I have no idea if there are any plans to allow DAS Return Times to be given out at WDW kiosks. If they do, I don't see it happening for some time. They just rolled out Fastpass Plus to include off-site guests in April 2024 and just recently expanded to allow more than 3 Fastpass Plus times.
I think it's too new and too many people have questions to make those CMs also responsible for DAS Return Times.
My ne'er standing about the 10 minutes off was the same as yours - to help account for the time spent in the Fastpass Line. The goal for the Fastpass lines is a wait of around 10 minutes or less once you enter the Fastpass line.
So, nothing to do with walking back to the line.