So...new spoilers for Treasure Vault came out recently (link to the section relevant to this post), and the guys in the video saw the swarming rune and kinda glossed over it, but I noticed something egregious pretty quickly.

For the record: it's etched onto a thrown weapon, and has a two-action, once-per-hour Activation where enemies in a 30-foot cone "take damage equal to double the weapon's number of damage dice." Note the quotation.

Knights of the Last Call (the guys in the video) read the rune probably as it was INTENDED to work, where a 1 striking swarming dagger would deal 4d4 damage in the area; not great, but it's something.

But, RAW, that's wrong. Reread the quotation. It wouldn't deal 4d4 damage in the area, it would deal 4 damage in the area. 4 AoE damage. For a level 9 rune. That is...so bad.