No harm powering up a few like 1-3 for regular usage unless is casual trainer who barely has enough stardust
Powering up to lvl 30 only need 80k which is not much. If u are semi hardcore player even maxing 1 is not much of a problem really
I got 1 maxed kyogre and 3 more above 30
U can argue groudon usage not that high and rhyperior only lags slightly behind but for kyogre the gap between it and its no2 is a massive GAP - a lvl 30 kyogre performs much faster than even a lvl 40 gyarados. If u been using the kyogre since last year then it’s already a great investment
Trainer Tip Nic made a good point in his latest video today
Right now Kyogre and Groudon don't come with their strongest moveset
However Origin Pulse for Kyogre and Precipice Blades for Groudon already found in game data
So likely in future will have Groudon and Kyogre day with these signature moves
Now just catch for candy and should not power up any kyogre or groudon