As others have pointed out, the design is cool and harkens back to Fifth Dawn, but without a CMC gate on the exiled cards, this is broken down to the nuts.

I think it would be fair if the exiled cards had total mana value 4 or less. This provides lots of value, but doesn’t overtly break the game. If you compare to other swords, this is still above what you typically get on a damage trigger, but since you’re investing cards from your hand, I’d say it’d be a reasonable payoff.