The effect has a really high ceiling for sure, but the floor is bad because you just dont end up in decks very often where you can be certain it will hurt your opponent more than you when you cast it
If you look closely at this card's set number, it's number 136 of 135 cards in the set, making it a special Secret Rare, an incredibly hard card to pull from packs thanks to a very low drop rate
Think Im wrong about Moxfield
Rhystic Study [Best Blue Tax Effect MTG Commander Staple] Rhystic Study stands as the premier card advantage engine in Commander, taxing opponents spells to fuel your hand
Dark is immune to Psychic - This is probably mostly just to weaken the Psychic type more than anything else, but it could possibly be a reference to how dark thoughts are hard to get rid of, such as addiction or depression, although that sends a fatalist message that you can't overcome your mental health problems, so I doubt that was something in mind when this was decided