Don't say "if this card attacks a defense position monster, inflict piercing damage to your opponent."
Say "piercing", at the top, before any other effect.
Fairy Meteor Crush would just say "the equipped monster has piercing."
Lots of archetypes have a theme effect, too, and they can use a keyword, too. Cards with more room can print reminder text in parentheses, basically saving that space for cards that don't have the room.
I'd like to add that the OCG formats its card text with bullet points which the TCG could easily adapt. Would make understanding the different effects of a single card a bit easier. But I also agree that the game could really benefit from keywords like MtG or Hearthstone.