I would say for Cosmic Power, the issue is that you're dedicating 2 move slots purely to defense. You need a way to make that dangerous, which as far as I know is limited exclusively to Stored Power sets. You'll spend 6 turns setting up, more if you need to heal, before you can actually attack. This gives your opponent all the time they need to switch for a Dark type (which is immune to Psychic, including Stored Power), and gives them the same amount of time to do their own setting up. Further, if you're raising your defenses, you probably already invested your Nature and EVs into defenses as well, so your Sp Attack will probably be mediocre.
There are a few Pokemon that can make it work, like Clefable, but it's certainly not the norm.