honestly terraforming mars isn't that complex, it's just really fucking difficult. the big things are heating is up A LOT (we know that part) and preventing the solar wind from sandblasting off the atmosphere. Like you can't really make mars worse, if it doesn't work you just keep trying.

meanwhile on earth we have stuff like "ecosystems" and "weather patterns" to consider and it's way harder to cool things down than it is to create heat.

it is however true that if we have the ability to terraform mars to a serious degree, we are basically guaranteed to have the different technology to fix earth.