Is kinda funny how things turn out.
If Valkyrimon had a 25% increase in supp he would be useful but by no means overpowered, since it doesn't boost Ceres/Cerbe/Sting healing. 15% Is so pathetic that you can have a better result just adding a little more def on your team.
If Piximon/Picklemon SP had Fairy's 50% increase it would be a good option, since requires the leader spot, so that 50% would have to compensate for the +1100/1300 That Ceres/Cerbe/Sting provide, it would not be easy, usually it would mean way less healing, but it would be a helpful option, and since Pixi and Valky are both Holy, the rune part would balance it alone, and even together would have problems to match those other 3 leaders.
Apocly is trickier since he is just another damage reducer, so he can't be much more powerful than Cranium with 25% on 3 turns, but a 15% damage reduction instead the lousy 10% that he has, would be actually helpful.
And yet, out of nowhere comes one of the best SP in terms of stats, with the best vampirism of the game that is basically a better healer than Ceres/Cerbe and a complement for strikers, with not more effort than having to wait a couple of weeks. #Balance