I don't think the recipe needs to be changed but I do understand why OP suggested that. Most of us aware that right now the ex loots (feather/heart/horn/whisker) are scarce on the market board because it's a monster loot and you can't get it unsynced which almost every people in game are doing it this way and no one (not even friends or fc) willing to spend time doing this synced, even when asked because it wasn't worth the time (wiping + RNG chance for loot).
A suggestion that I could think of is to include it into the treasure chest along with the pony -or- add a small chance that you can yield the loot via desynthesis of the accessory/weapon that you can get from the ex run.
