In addition to their wood bonus, they will now also receive some stone.
This will give them the option to use powerful MAA into towers or place a defensive tower while still dropping TCs.
The bonus is more valuable in the late game, providing a resource that continues to be important even in Imperial Age where wood is not as crucial.
With both wood and stone in Castle Age, they can potentially drop more TCs or additional buildings like a workshop, university, or monastery.
It also allows for the possibility to sell the stone in a fast castle build for a more competitive uptime.
Overall, this bonus is a flexible boost for them in both open and closed maps without making them too overpowered in hybrid and water maps where they are already strong.