The only caveat is that the card must be banished in order to perform the healing ability
When its defeated, exile it, then cast it transformed.) When this Siege enters, destroy target non-Elf creature an opponent controls with power X or less, where X is the number of lands you control
The decision was deemed acceptable because the worst case scenario for player mistakes isn't that bad - you tell the player with Lutri in the companion slot that he's banned, and they drop him into the 99
This Oketras double strike and the vigilance its tokens have also make it a good fit for Odric, Lunarch Marshal keyword soup
If I told you the blue player got free instants or sorceries, would you say they stand a good a chance
That said, one MTG card did get Banned in Vintage