It's wrong to think of this as Dickey vs. Hutchison. It's amazing how fast a lucky half season can make people ignorant of injuries. An extension would be about Dickey vs. Scott Diamond. I'd like to see the team continue adding viable starters even if we extend him and have 6.
Also, your average backup catcher is replacement level (0 WAR, no surprise). You're exaggerating the gap quite a bit. Hell, give Thole a normal BABIP and he IS average