Not that simple. When carbon in the soil rises beyond a certain percentage (a tree falls) it'll convert back to CO2 because of the bugs eating it. But if the percentage starts at zero (in a desert) and an ecosystem settles there, the percentage will rise and stay above zero for as long as the ecosystem survives. Basically the plants generate matter as fast as wildlife eats it.
This sequestration can be long term if things go well or it can be short term if plants die in large numbers (because of climate change, diseases...).
Trees excel at harvesting water. When you water a tree, there is evaporative cooling like an artificial cooler but during the night, the dew falls back on the leaves and the ground where some of it finds its way back to the trees (possibly via an invertebrate first). Also the reflectiveness of leaves helps. Then there's the soil where layers of dead leaves, wood and others accumulate, sequester CO2 and create a sponge. Finally, by virtue of making the region cooler, rain is more likely to fall. Humans can probably engineer something better but the bar is high.
Regarding (b): I think an employee working day to day gets a much better picture than investors. It requires time on the job, but my point is that it's not as one-sided as you make seem.
This sequestration can be long term if things go well or it can be short term if plants die in large numbers (because of climate change, diseases...).