I think PP was trying to say that after you wait the posted wait time minus 10 minutes you will still have to wait through the FP+ (at WDW) queue, however long that happens to be at the time. OP mentioned inability to stand without constant pain and shortening wait times, PP was explaining that waiting in the line is not completely bypassed.
At DL they also use the FP entrance, but not as many rides have one. However, there are often lines formed at the accessible entrances for wheelchairs and
DAS returns, so the waiting in line part still applies. Even if you're in a wheelchair and they give you a return time slip, you still return to wait in a line with other wheelchair return time recipients and DAS returners.