Even if you cover the whole planet in forests, there is a finite amount of fossil fuels you can burn before it is negated.
I think that this is the crux of the matter, and of course you're right. The total amount of carbon stored in fossil fuels is (presumably, without searching for the numbers) much greater than the amount currently stored in living organisms, so there is a finite amount of fossil fuels that can be burnt before the carbon emissions exceed the capacity of forests/vegetation to capture it. Do you know what that "finite amount of fossil fuels" would be? From what I have seen, it is quite large, though humanity is rapidly approaching it. What's needed is for the rate of emissions to be reduced below the rate of capture, and so a reduction in fossil fuel use is urgently needed, but I wouldn't say that completely eliminating fossil fuel use is more important than protecting forests. All that's needed in the long term is for carbon capture to at least equal carbon emissions. In the short term, the planet is already close enough to the "point of no return" that reforestation is necessary in order to bring down levels of carbon dioxide, regardless of how quickly fossil use ceases. It has to be both. Burning fossil fuels is not a sustainable way to meet the energy needs of 8 billion+ humans. Cutting down forests for biofuel is not a sustainable way to meet the energy needs of 8 billion+ humans. Deforestation for biofuel would be sustainable for a much larger population than would burning fossil fuels (due to the extremely slow renewal rate of fossil fuels), but we're past that point. There's not enough land. Either energy consumption needs to drastically decrease, or non-combustion sources of energy are needed.
I get the impression that we are essentially "on the same side" and just quibbling over details. You make an excellent case against fossil fuels! Looking at it in terms of the broader carbon cycle makes the necessity of ending fossil fuel use very obvious even ignoring any concerns about pollution, destructive extraction practices, or other harmful effects.
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