It's also how we got all the carbon in our top soils. A 6 inch or more covering of carbon (mixed with minerals etc) covering huge parts of the earth's surface.

Planting trees, harvesting them, and turning them by pyrolysis into biochar/charcoal and then burying it can partially restore these soils and sequester carbon at the same time.

Yep, but it is a nontrivial amount of work to produce approximately as much biochar as we have burnt coal.

Oh, absolutely. It would take generations. But taking forestry waste and turning it into a soil amendment is a worthwhile endeavour even from the POV of improving food production.