Historic is not the same format it was just a couple days ago. In terms of foundational cards, the balance between Strixhaven's Mystical Archive and Jumpstart: Historic Horizons is extremely close. That's a wild statement to make when we're talking about a set that added literal Brainstorm to the format and has already produced multiple bans, but I've got an even wilder one on deck for you.
It's possible that Jumpstart: Historic Horizons has even more potential than the Mystical Archive to break the Historic format. Sure, Brainstorm empowered blue to a ridiculous degree, but it was always just a means to an end. Jumpstart: Historic Horizons contains some cards that take the general rules of Magic: The Gathering very lightly. High on that list has to be Throes of Chaos — a card which elevates doing nothing to an absolute artform. In conjunction with Tibalt's Trickery, this card gets up to some real nonsense, and not in a way that creates appealing games of Magic.
And yet, this isn't even the most broken interaction in the set.
Davriel's Withering targeting your own Vesperlark moves the Vesperlark from the graveyard to the battlefield as many times as you would like (and potentially more, forcing you to draw games where Vesperlark is your only returnable target and you aren't benefitting from the loop), meaning that any kind of effect that triggers upon the death of a creature or the entrance of a creature to the battlefield is going to do its thing to the nth degree. A three-card creature-based combo isn't the most appealing setup in most scenarios, but Davriel's Withering is just a solid removal spell in the Historic context, and with enough work in deckbuilding, Vesperlark can carry its weight as well.