I think the hills on the alternate westbound are a bit worse than the Custis Trail. However, once you no longer need your cue sheet (because you have internalized the route) and you factor in that you don’t have to stop all the time for peds, I think the route is easier. I agree that the worst spot in general is 16th St, pavement is kind of bad. However, in general I think the streets are smoother than the Custis Trail, only a few parts of which have been recently repaved.
I still ask myself, what is so attractive to walkers and runners about the Custis? Most of it is next to a freeway! I would never walk/jog along that unless the other choices were really bad.