I think you and parent comment might actually agree. The 3x trees is an indication of too much, too many small trees, too much fuel. Places that burn and recover lose their "excess" trees. The trees get more space and are healthy top to bottom.
OTOH, tree farm trees are bred to have few branches and are planted very close together. Tree farms grow tree trunks, not trees.
There is a line of thought, which honestly I think comes from the timber industry, that growing trees are a bigger carbon sink than existing trees. They do argue that the tree farm is actually better because it is growing. I'm extremely skeptical of that claim. Particularly skeptical because the trees in tree farms are so unhealthy, the total amount of green vegetative surface on them is confined to a small canopy and has no vertical depth.
In comparison, old growth vs tree farm is night and day for ecology. Tree farms are very dense, rodents thrive in them but not necessarily much else. Old growth OTOH is generally a pleasure to walk through.
> I would expect a few old growth trees in an acre would be a substantially better forest
There's indeed a mixture of ages unless we are talking a tree farm. A tree farm is a mono-culture with trees approximately the same age all growing like Q-tips together.
Old growth trees are fire resistant. The younger ones trees get overshaded and don't grow, or they burn down before they get tall enough. The young trees that do survive, they go on to become the next generation of old growth trees.
(My experience on the subject: extensive time camping & bikepacking in Northwest forests, I've traveled through a several thousand miles of northwest forests in the last 10 years)