Only if Primal Kyogre drops as well. You actually cannot tell me with a straight face that Primal Groudon should be ranked below Primal Kyogre. Groudon has more CP than Kyogre for a reason; just look at the dynamics of the matchup (going past the 1v1 because we need to look at this beyond the vacuum). If Kyogre switches in on Groudon, Precipice Blades is unaffected by Primordial Sea. If Groudon switches in on Kyogre, Water Spout / Origin Pulse / Scald etc. fails. As I think you can see here, one of these is more readily able to switch in. Another thing is that resisting Xerneas is a huge asset to have, given that Xerneas is the only Restricted to outrank Groudon in total CP earned.Primal Groupon: S to A. Although it continues to be a prominent force in the meta, the increasingly popular RayOgre has taken its toll on it.
On the topic of Restricted pairs, Pokemon that used to be paired next to Kyogre are now largely teaming up with Groudon; just look at Xerneas and Lunala.
I'll hold off on saying whether or not Groudon should be S, but there is absolutely no way it should be ranked below Kyogre. Groudon is simply better, end of discussion.