Excellent commentary, all. Most important, best wishes for Felipe and Sam!
Having ridden the routes they were on in California, and those in Dakar (and Morocco) for reference, I can say that our US riding is generally considerably more risky and technical. As well, the roadbooks here don't have dangers marked- they are as good or better in terms of directional layout, but they make no attempt to call out dangers.
That's a big difference for the frontrunners in Dakar- what I witnessed there was commitment beyond visibility, and total trust in the danger markings of the roadbook.
I'm a bit stunned they would be doing testing in December- no time for recovery, and not much for fixing anything substantive on the bike.