Well, keep in mind that the rivers somewhat act against the roads, because you need to cross the rivers at a ford or bridge, and that provides a natural funnel-point that defenders can use against you, as we’ve seen with the Battle of the Fords.
I would say that there are mechanisms for moderating the potential threat from a road network: first, use a riverrine navy to ensure that you have the better interior lines, second, build castles at strategic points along the road network to slow the enemy’s progress and whittle down their numbers through multiple sieges, third, build a lot of swing bridges on crossing points so that you can maximize your own flexibility vis-a-vis travel on road vs. travel on water and potentially cut off your enemy by denying them a crossing.