Well especially since the nerfing of zombies range, the shadow defense isn't the most important as dodging zombie attacks has become much easier. Also for the actual boss battle you shouldn't be fighting many zombies so its no big deal.

The stun resistance is nice but I find that I can dodge the ceiling attacks easily enough for it not to be a problem.

Here is where your shield will start to fall down: During stages 2 and 4 of Vanaduke he will unleash bullet hell. These bullets deal elemental and they aren't the easiest thing to dodge (especially if, like me, you have latency issues). That is why having some elemental defense is good on your shield, which is why the majority of firestorm citadel runners choose the grey owlite.

So your shield is perfectly good for firestorm citadel, but it it not the optimal shield (if you are being picky about endgame items).