Meltdowner power would be awesome in destruction work (buildings for example?), escavating, drilling, and so on.
Since she trully vaporises the matter, rather than just displacing it, that would save even more ressources.
But Mikoto's power is a lot more versatile as she can use it from fine manipulations like server hacking to moving tons of metal scrapes, weapons, walking on walls and so on. Her range of possible is clearly vastly superior to what Meltdowner showed us.