Sevvy and Kreoss both have antimagic items that make Spellshield not necessary, and both benefit more from an Arc Node anyway.
Reclaimer can smoke to keep shooting at bay.
Amon and the Harbinger NEED to be protected from shooting. Amon is squishy and the harby is a parade fload. Having multiple small jacks makes Amon's synergy more worthwhile which is why they get used. Defensive Strike is handy but not game breaking.
If you don't plan on using either of these casters, the Devout is nice but not necessary. If you want to broaden your horizons to include these two then I'd definately recommend picking one up. I run two with Amon.