To keep it short and sweet: let's be completely real here, Celestial Shield is currently the worst (complete) shield in the game besides Iron Buckler and Scale Shield. Yes, the very worst, worse than all the other 1*, 2*, 3*, 4*, and 5* shields, and even worse than Proto Shield (Proto Shield can not shield bump, thus allowing a player to freely abuse shield cancels, which is one certain niche that it fills, whereas Celestial Shield has none). It has been proven time and time again that not only are status resistances really the most important factor of a shield defensively, but the second-most important factor is having solid Normal defense. Celestial Shield has neither of these things. It needs something to be done to it, so I'm suggesting that it be given Stun resistance and/or Curse resistance.

Not only would this give the shield one specific use (that being Shadow Firestorm Citadel), it would give it something that no other shield has, Curse resistance, making it unique. This also ties in with the lore of the shield; "Cradle's equinox inspired the dual nature of this specialist shield, which protects against the dazzling light of day [stun could very well work here just as well as piercing could] and the chill of the night [curse could very well work here just as well as shadow does] in equal measure."

Also, this would not heavily effect the shield, as it only really allows it to fill one particular role-- being as a shield for UFSC, where many players would probably prefer a Normal/Fire defense shield regardless assuming they even had access to Celestial Shield. But filling one specific role is still better than being a completely useless antique.

So just to sum it up, give Celestial Shield either Stun or Curse defense, or give it both. It's a step in the right direction for balance, at the very least....