Definitive Sources

[L Verge]

This is just my personal opinion, but Powell would have stuck out like a sore thumb on the escape route.

Just like he stands out in photos for us, he was likely just as easily identified by strangers in 1865. The folks along the escape route had not laid eyes on him (I'm guessing not even Harbin). His strength, height, etc. was unusual for the time whereas Herold was just "average" - and probably known by some on the route. Also, it becomes more difficult to travel and remain hidden the more people that are in a group. One person usually has an easier time, but Herold was needed for his "environmental" knowledge.

Powell, on the other hand, was trained to stand and fight and then skedaddle. He also had vital contacts in Baltimore and was much more familiar with that city. I just don't see him even considering sticking with Booth to the end. I'm amazed that Herold did!