Depopulation only works on average.

I presume land ownership is according to a power law (~money). Perhaps just need to "depopulate" extremely large land owners?

Terraforming takes centuries and trillions. Depopulation is super easy. Just provide a minimum level of education, opportunity and contraception and significantly more people choose not to have kids.

Not sure if our economies can survive that way though.

Neither seems realistic or achievable, except the latter by nuclear armageddon.

Depopulation is super easy. Provide universal access to contraception and give people the choice to not have babies. Evidence shows that works.