I know, i like i said, it's rare. And looking into this it really depends on if Groundon comes out second with Physical of Special Moveset.
If Groundon comes out before Kyogre he's screwed.
If Groundon comes out after Kyogre and he has a Special set, it's pretty even
And If Groudon comes out after Kyogre with a Physical he more than likely is to win
That's how i see it at the moment