This is an interesting card. When I first looked at it, my knee jerk reaction was negative. A card that destroys all nonland permanents except for two of your opponents that get returned to their hand seems really poor in reality. That being said, Planar Cleansing was a great card when it was legal, and aside from being a bit more taxing on the mana, I don’t think Devastating Mastery should be that different.
There are some corner cases where you actually want to play the card for 2WW. The most notable case would be against a hyper aggressive creature deck when you simply need to clear the board as early as turn four. It’s unclear how likely it is that you’ll actually win those games, but still more likely than just dying with a six-mana card in your hand that you can’t cast.
Overall, I’m thinking of this as a six-mana Planar Cleansing-like sweeper, with very minor upside. It’s probably less upside than the increase in colored mana is worth, but it’s probably still strong enough to play in controlling decks.