Sure it is. First off, you gain 25% from just Shellra V. That's half of your cap right there. Then you've got Twilight Torque and Defending Ring bringing you up to 40%, a good Dark Ring bringing you up to 44~46%, and from there 4% is not hard to find.

If you're going straight to 50% from 0, then yes, that's difficult for non-tanks. Good thing Shell V covers half the gap, unlike Protect only raising Defense.