The point is that the greenhouse gases that they emit have already been captured from the atmosphere, which makes them carbon neutral.

I’m on board with the rest of your argument, but that’s a very reductionist way to look at things. The concern with biofuel usage is, that there is inevitably going to be methane emissions, which is a much more potent greenhouse gas than CO2. So the zero sum game doesn’t really apply here.

On top of that, it’s comparatively inefficient, among other issues.

I wouldn’t bet on biomass to play a large role in a carbon neutral energy system.