Which kyogre to power up?
98 14 Atk 15 Def 15 Sta
96 15 Atk 13 Def 15 Sta
Answers
No one is saying they're certain, everyone knows catching a 100% legend is extremely rare. But what they're trying to say is you should at least try for a better Kyogre (no matter how small the chance) before it leaves, because there is no rush to power it up. Now is the time for powering up your electric types to counter Kyogre. Very simple concept really.
Kyogre has high base stats and a high power fast move so breakpoints are less detrimental to it. You can't go too wrong either way if you want the highest total percentage, highest attack, or maybe judge by highest CP.
Even if there is a breakpoint that the 14 atk IV misses, it would only be ~5% difference. (Compared with lower power fast moves where a breakpoint can be ~20% difference.)
If one of the candidates currently has Thunder, I suppose that could be an additional advantage to consider. That is useful now against other Kyogre raids, then TM later to Hydro Pump.
Exactly what I did. Two powered up with Thunder, and when it's important, I'll TM them to something useful (HydroPump).
But unless there's a pressing reason to power a legendary up now (like using it), wait until they are gone, and then decide what to do. I powered up a SB Groudon to use against non-SB Groudons, and Thunder Kyogre. I have three strong Dragonites, so I doubt I'll need to power up a DT/O Rayquaza to use against other Rayquaza, since Ice is generally more effective, unless it's windy out. But if I find I need one, I'll power a good one up before they are gone to use. Otherwise, wait until the cycle is done, and then make an intelligent decision with all the information available.
I don't agree that atk IV is more important for low power fast moves.
While a missed breakpoint might make difference of 20% for a low power move and just 10% for a high power one, the likelihood of a decisive breakpoint at level 40 for the high power one is twice as high as the low power one.
A breakpoint might have a huge impact for Fury Cutter, but you won't see any breakpoints most of the time. From a statistical point of view the power of a fast move is irrelevant for the importance of atk IV.
What about Yawn? It's a very low power fast move. Is atk IV relevant for this one? ;-)