Actually, she's a lot more flexible than she appears, but is incredibly dependant on her team to really maximize everything. Foresight is incredible for ruining people's aimed blasts (or up-close and personal attacks). Levitation makes non-mobile teams happy (use with Proletariat and watch them fly across the mountains!) The decoy is a great defensive card for utterly frustrating anyone dependant on melee combat (against the Operative, the Visionary is probably the most frustrating opponent). Her Demoralize is great for setting opponents up to fail. Since the Maelstrom doesn't target allies (or require line of sight), you can lurk behind buildings and generally lure your opponents out.
Twist the Ether is fantastic for offense or defense, since it can be used for your allies as well as enemies.
Basically, Visionary can be used to wreck just about anyone's carefuly contructed plan and disrupt the field for her allies to follow up on. My favorite thing to do is to rock Foresight and Twist the Ether, and stay behind my allies. It adds up.