There are a couple of other things that point to "replacement legs," such as the time of departure from the pit stop was a rare nighttime departure which has been uncommon since TAR moved to filming in HD. Then in TAR 4, the legs were sufficiently planned to allow teams to self drive rather than use taxis during the leg. (Production would have had to arrange for Fords to be available for driving, since Ford is now a sponsor and we know that navigation is always a way to spread teams out.)
The detour task was fine for the location and the fact that it called for teams to use skills they might not have had. Some teams simply assembled their rafts poorly, or didn't properly move the raft in the water (which meant a lack of experience.) I can't recall any physical task where the Cowboys aren't fast. We've known this since their original season, and they're very consistent about this.
The roadblock was a psych out of the teams since they might not realize what the roadblock actually was, so while it might have been only a part of the waterfall to reach the clue, you still needed to get to the clues to grab one.
It's clear there was some order shuffling in the taxis both to the airport after leaving the pitstop, and during the leg. Joey and Meghan's downfall was releasing the taxi when they reached the roadblock location; I think they would have survived but for that mistake.