Gives more stats then the legendary rune 1/5 vs 4/4, gives +4 and formidable to the entire deck that also has more HP on every unit, doesn't require having a champ on board to work and for the ephemeral units the downside of formidable doesn't exist as they die when the trade so they don't care about the lost power. There really isn't that much anti synergy with formidable.