If you aren't getting anything out of the response, it's overcosted by one resource, or maybe a little more. The X-men trait does have synergy value, but you probably need multiple synergy effects to outweigh the amount you're overpaying.
A typical scenario might be around 20% star-boost cards, so if you're blind-firing this, you're going to miss frequently. You may play cards that let you scout and/or rearrange the encounter deck, e.g. Blindfold. Even if you can't find a star-boost to set up a killshot, you may still want to trigger Longshot's response just to move a card out of the way for later.
If you hit with the effect, it could be doing as little as one damage (if you were attacking a 3 HP minion), or as much as 11 or more (Blob with a fresh Homo Superior). I'd say if you can get an effective 3 damage out of the effect, it's overcome the amount you overpaid for it up front to become a reasonable value.
Overall, I think I like it; it's reasonably average if the game is going normally, but has the potential to be massively impactful in the toughest scenarios and ugliest game states, especially if you build in some helper cards. A+ for theme, maybe a B for gameplay?