In some climate zones, grasslands do it better than forests.
https://climatechange.ucdavis.edu/climate/news/grasslands-mo...
You can make paper products including things like cardboard and packaging.
You can put livestock on it and produce meat.
Or if you just want to sequester carbon, you can harvest it and bury it deep in the ground.
If you use grasslands for grazing cattle you get meat, or also wool with sheep. Sequestering carbon into grassland soil (or into any soil, really) makes them better at absorbing and retaining rainwater, reducing the risks of catastrophic floods in the watershed area.
And the GP is quite wrong, because almost everything will be more efficient than trees or grass. Machines are just way more expensive, that's why nobody ever made them.
Some places can plant trees, others grasslands. Or whatever, but it seems like there is a lot of money to create an industrial process that can be commercialized instead of just doing the work naturally...