Noting your comments that subspear is too far for an annual progress, would Robert have even survived a trip to Dornr with less than a full court?

Sunspear is too far for a normal progress of 2-3 months, but it’s not too far for an annual progress. Aerys II visited Dorne in 270 AC, after all. However, I would guess that it’s more likely that the trip was done by ship (10 days on average) rather than on horse (almost seven months).