Spoiler

Okay, so the problem here is that the Japanese use the same word for Ground and Grand. Groundion makes sense since there's a SeaLeon and a Skion, but GoseiGround not so much. It's like they forgot to tell the card maker that they're making a pun and that it was supposed to be GoseiGrand (it's grand on the gosei website)
GoseiGrand is a more logical step from GoseiGreat, plus even though it's made of Groundion, it's also made of a sky and sea part, so it's no longer exclusively ground.