This is a super narrow pessimistic viewpoint that is rife with agenda pushing. We do not know if the wealthy years of the 20th century are over yet. Neo-feudalism is possible, but unlikely to be the same conditions as the middle-ages standard of work until you drop dead.

Not every single problem in society is fixed by getting off fossil fuels. "Decoupling" the economy from fossil fuels will not be a magic solution in this case.