This looks fairly dramatic in a vacuum, but in reality, its the kind of post-release adjustment we often see with pricey mythics
The reason for the ban is the huge upside of combo decks gaining a ton of resources and basically drawing their entire decks
Sure, a measly +1/+1 counter doesn't seem like much, but when you have the deck built around it and include graft cards like Plaxcaster Frogling and Helium Squirter, you can really start doing your opponents some favours, which of course is the number one way to ingratiate yourself to those who might otherwise wish to do you harm
Put each playtest card among them into your hand
Play a few games of Jumpstart , and you might find grave-bound Gixians using Urza's powerstones, or Mishra's mighty machines teaming up with Titania's Argothian defenses
But you also arent playing ridiculous combos with cards most people have never seen before when you pick those easy commanders