What I would personally do, is instead of having the Guildpack be just one guild, have it be either 3 cards each from 5 different guilds or 5 cards each from 3 different guilds. That way you still have 15 cards per pack, but players have a bit more freedom choosing which guild to draft.
Expanding on this idea, players could choose a guild, then take all, for example, 3 cards of that guild from their pack, then pass it to the next player, who would do the same.
I want you to give me legends that never got a card: creatures, planewalkers, lands, etc. It doesn't matter what. Then I will try to make a balanced, lore-friendly card that looks good and works well.
Expanding on this idea, players could choose a guild, then take all, for example, 3 cards of that guild from their pack, then pass it to the next player, who would do the same.
EDIT: Forgot some words