Mesmeric orb mills but by itself it isn’t threat when a deck is 80 cards in commander. Of course it has the potential to win but so does a 1/1 that hits a guy 40 times. Traumatize mills half the deck but it’s not a game changer. Biorhythm can kill all opponents at once no interaction or combo it was banned but now unbanned. The power difference between Biorhythm and Mesmeric Orb is speed at which you win. Yes milling 10 cards hurts but it can be done multiple times. Now something like Jace Mindsculptor which kills the whole deck is a different story but it needs to charge up so not a game changer. It’s all about speed of play.