Its broken with Moxes, with cantrips, with Gush, with pitch spells, the list goes on and on, and thats to say nothing of how broken it is with Time Walk
Milling random cards will give pseudo card quality or card advantage, or it can be a mana saving too
Mono-Green Devotion 12 Forest 4 Outcaster Trailblazer 4 Invasion of Ixalan 4 Leyline of the Guildpact 4 Storm the Festival 4 Cavalier of Thorns 4 Kiora, Behemoth Beckoner 4 Nykthos, Shrine to Nyx 4 Old-Growth Troll 4 Elvish Mystic 4 Llanowar Elves 3 Lair of the Hydra 2 Boseiju, Who Endures 2 Ulvenwald Oddity 1 Oath of Nissa 3 The Stone Brain 2 Arasta of the Endless Web 2 Unlicensed Hearse 2 Keen-Eyed Curator 2 Scrapshooter 1 Emrakul, the Promised End 1 Cityscape Leveler 1 Obstinate Baloth 1 Prowling Serpopard Mono-Green Devotion is only a small part of the winner's metagame, but it is capable of amazing openings
This makes it less flexible than Past in Flames, but potentially much more powerful