The rarity of Mystical Archives is flustering for three major reasons
Alpha Cards For the most part, Alpha cards are exactly the same as all other Magic: The Gathering cards, with one major exception
All in all, Summon: Bahamut has been a more competitive card than players expected, rocketing the card to fifth on our list
Its name or flavour text aren't really indicative of what it is, and the great creature update isn't much helpful by classifying this thing as the very ambiguous 'Beast'
You could Rule 0 both Chandra, Fire of Kaladesh and Nissa, Vastwood Seer as Partner commanders, but that feels against the spirit of a deckbuilding challenge
If and when that happens this will just to at least a 7/10 card