I would just take your Kyogre up a very few levels (although you might have more stardust than RC). Legendaries getting better/exclusive moves isn’t ever going to make that Gyarados as good that Kyogre 1.0. Even if you get a better Kyogre in a year...that’s a year of making your current Kyogre a little stronger and using it. Not talking anywhere near max, but just a little bump and stop well before the RC cost gets sky high
Gyarados or Rhydon
I successfully raided a boosted Flareon on my second attempt. It was one with flamethrower, so the difference was making a few dodges. I still feel like I need 1 more pokemon going forward. Here was the team I used...
Level 40 SD/SE Tyranitar
Level 30 WF/HP Kyrogre
Level 40 WF/HP Gyarados
Level 40 MS/SE Rhydon
Level 28.5 WF/HP Gyarados
2505 CP RT/RB Golem
I could invest in a Golem, which would help me in partly cloudy, but a Rhydon would be boosted against a boosted Flareon. The big thing is I never got a Groudon and don't have a maxed ground Rhydon. Rhydon also has the benefit of an evolution in gen 4. Would it make more sense to invest in a Rhydon or Gyarados...or something else? Thanks
Answers
I've done that, and I must say I don't use Mewtwo nearly as much as Kyogre for solo raids. It's a good filler, but way behind the optimized counters that usually front-load my solo teams. Also, the difference between a L30 and a L35 Kyogre is enormous in terms of performance and time to win... beyond that it's way too expensive candy wise. So I agree with devshaw on this, but of course do what you feel is good for your playstyle!
Mewtwo is an optimal or great counter for a lot of solo raids though.
Donphan is going to be the first time I use Kyogre for solos since Claydol because personally I do solos without legendaries if I can. Meanwhile Mewtwo was necessary for me to do unique challenges against Jolteon and the Showdown bosses.
Rhydon isn't a viable Flareon counter without the weather boost and even in Sunny it barely makes the cut to below 180s TTW at level 40. Considering this, it doesn't make sense to invest in it just because it evolves. You can do that later if Rhyperior does turn out to be good.
The best thing to invest in for Flareon raids would be another level 30 Kyogre, followed by getting another Tyranitar or Gyarados to level 35 or so.