In terms of the physical weight/volume of resources terraforming probably would be order of magnitudes more. But if terraforming involves mostly releasing froze

In terms of the physical weight/volume of resources terraforming probably would be order of magnitudes more. But if terraforming involves mostly releasing frozen and underground stores of gasses, well that's potentially cheaper than building giant vacuum-sealed dome cities. And as a result you get the whole surface as a habitat (in the long run).