I choose the palfrey for the 1 extra speed, apparently I didn't really compare the stats or I might have taken the rouncey.
I think moving the speed from 42 to 43 would work, or giving it 42 maneuver.
But honestly to stay consistent with my views, I think they should just leave it alone. That 1 extra speed makes it the fastest horse besides the courser. That's significant enough for some people to pick it over the rouncey (as I did).