The fact that the board can become rather full in Modern, Jace can often be out raced before he even hits the board which is the main reason Jace doesnt see more play
For example, Lady Miss Park Avenue is Amber and Emerald
Just one more draw source and you ruin another players night
If you havent heard about the first person in the world to win a full playset of Stitch, Rock Star, well, thats me
Balefire Liege, Blinking Spirit, Tradewind Rider, Spirit of the Night, Spirit of the Hearth, Azorius Herald, Bloodghast, Nether Shadow, Nether Spirit, Nether Traitor, Krovikan Horror, Celestial Crusader, all of the Spirit avatars like Demigod of Revenge, Primordial Sage, Dimir Infiltrator, the muse cycle like Windborn Muse and Seedborn Muse, Eternal Dragon, Ghost Council of Orzhova, Guardian of the Guildpact, Swans of Bryn Argoll, Wall of Reverence, Karmic Guide, Midnight Banshee, the Phantom creatures like Phantom Centaur and Phantom Nishoba, the Rusalkas, the Eidolons, both Spirit Guides, Sovereigns of Lost Alara, Spectral Lynx, and, of course, Will-o'-the-Wisp
Cards that are good enough to regularly make decks, but ones that dont completely outshine the competition