Primal / Mega Legendary Abilities

I'm going to ask a really stupid question, because I did not see it asked before.

Let's say Kyogre enters battle against a Groudon, and both can undergo Primal Reversion.

Is it better to have a faster Kyogre (because Primordial Sea prevents desolate land from taking hold), or a slower Kyogre (because it is the last condition to take hold)?

In addition, how does Rayqaza's Delta Stream affect, or be affected by, Primordial Sea / Desolate Land?

The last condition will be the one taking effect, just like normal weathers. So for example, if both Primals are switched into the field, the slower mon's ability will be the one that lasts. If they are both same speed, it all is 50/50 and depends on speed tie, and whoever happens to lose that tie for that turn gets its weather up. This is pretty much why Primal Groudon is a broken piece of land behemoth while Primal Kyogre got the short end of the stick. Primaldon can switch into Kyogre's water attacks anytime, while switching into Primaldon's signature ground attack with Kyogre is almost a guaranteed OHKO. I'd still make Kyogre as fast as it could so you can revenge kill a Primal Groudon instead of being slow because it gets mauled by Groudon's Ground attacks anyways if both are on the field. Primal Kyogre is one of the few monsters that can OHKO Primal Groudon, if it comes in on the right moment.

Rayquaza's Delta Stream just completely cancels out Primal mon's abilities as long as it is on the field. Therefore, if you have Surf on Mega Rayquaza, it will hit Primal Groudon anyways.

Sorry for the bump.

Delta Stream also removes all Flying type weaknesses from M Rayquaza, so, for ex. an Ice move now does 2x damage instead of 4x damage.