The design of five color generals has changed so substantially over the last few years that I believe that a ban like this was inevitable
On her own, shes already annoying, a two-turn Dig Through Time glued to a three-mana planeswalker
This deck features 20+ counterspell spells (instants), and in addition a number of your creatures add additional counter abilities, such as Voidmage Prodigy, which can turn each of your wizards into a counterspell
You've got 40 creatures (aside from your commander) and 39 lands to ensure a decent opening hand
Possibility Storm resolves first, giving you a different, random artifact from your deck for free
The first Mystery Dungeon games received decidedly mixed critic reviews, but still sold over 1.4 million copies in Japan alone