I am currently playing a multiplayer game with some friends and we were testing out the various visions. I'm going with a golem build, another is going for a sort of healer type build, you get the idea, we all have different builds. One player goes Shadow and takes Vision of Ruin - shadow.
The effects are, as follows. Spoilers
You can read about them in the images below.
Now, there is a pretty big difference in what they world effects do. Astral ironically enough benefits most of the players by giving them an additional spell per turn even if the prophet can basically cast double the spells at the same price in casting points.
Chaos makes all non-allied factions go to war, but by that time you've probably already drawn the battle lines on who is friend and who is foe, and they get power from slaughter which doesn't really affect anything.
Then we get to Shadow, which absolutely is detrimental to every player in the world that isn't also rocking undead. A 50% nerf to healing can turn a +40 heal into a +20. A 15 to a 7-8. (Most of the time undead factions don't have to worry too much about healing since well.. they basically just revive their dead anyway) On top of that, the prophet gets a battle effect that essentially increases their troop count by the amount of enemies they have without any downsides to it. The cherry on top, the +20 free souls they get per turn.
Astral and Chaos do not really screw over the other players in the lobby like Shadow does, and shadow is the EASIEST to achieve. What's more, there is nothing you can do to prevent it, no counter-play, no countermeasures you can put into effect. You're just kinda screwed over if you're not playing undead. There are way too many bonuses tied to Vision of Ruin - Shadow, and I do believe it needs to be toned down, especially for how easy it is to get and how powerful the effects are.