Also given the fact the powerups are evenly distributed on the stage, not sure how anyone will benefit more than others
They are not evenly distributed on the stage.
Some players may have two or three blocks to break before reaching a desirable powerup. Some players may have five or eight or so blocks before reaching a desirable powerup. Sometimes players are surrounded by debuffs, other times they are surrounded by all the best.
Some of the powerups are rare with only one or two on a level, so if their contents are visible will be immediately clear that those are going to specific people based entirely on their starting point. A player who starts next to accelerators and a remote control can blow up blocks much more rapidly than those who need to wait around, so players may sprint directly to those items, and they'll leave behind the debuffs until they find a way to infect others with them.
If I start the game and can immediately see I'm surrounded by junk while my opponent is surrounded by awesome, I'm going to ragequit. If I can't see the contents but I can see I've got two powerups nearby and my opponent has seven, I'm going to ragequit.
The current implementation actually helps the game. The game is heavily impacted by the placement being randomly unfair. But because players don't know until they they try, the game becomes random rewards rather than something you can plan. Random rewards FEEL good even if they aren't evenly balanced, so players enjoy them more than they would with visible placement. Visible placement of random distribution often will FEEL unfair (because they aren't evenly balanced) so people wouldn't enjoy the game as much.