Meteo is always kind of a huge deal in FF games, it's just not always huge enough to wipe out a planet. Holy is pretty much the same way, since it's the only white spell that can really do damage, and it's useful against lots of nasty enemies. As far as green liquid.... Well.... It's sort of unclear that that's the effect of Holy. All we really know is that it's the lifestream attempting to stop Meteo (it explains that the planet does this in the game).