i used to use Ghost Kill tactics in my early playing. I managed to bring it to level 4 too, but now i use Sun Move.

On long term Ghost Kill tactics is a tactics you can run only if you are a whale, otherwise you absolutely need a more defensive tile.

At level 6 you'll begin to feel the difference between not owning that 990 resistance, because the attack/ninjutsu tiles are useless if you are under chaos/immobile/sleep while defense/resistance/hp tiles are useful even when you are under those statuses.