As for wood, it would probably still be better to go after standing forests for large amounts of wood. If a given tree takes five years to reach large size, and ten years to advance a size category, then a baseline can probably be established for how much wood would be obtained. I'm not sure how much wood is actually gained from a tree of a given size, or how much would be needed for various activities, so I can't give a statistical analysis. It would seem likely that the advantage of the trees for wood production would only emerge over time, though, when harvesting wood from forests is just too dangerous or when there isn't any wood to harvest from them.
Alternatively, it could be noted that the last known example of these trees (outside of the High Marches and Northern Island, which are effectively too dangerous to enter) were destroyed when an unknown creature attacked and destroyed the settlement on the Southern Island, which previously played host to a farm for these. It would still let the statblock fill it's purpose(giving an idea of how dangerous the region is), while not letting them be taken advantage of.