Totally different cameras. Surely you mean to compare the fuji gx680 to the rz? The 617 format is very specialized.
And... as everyone has said... no piece of gear, alone, is going to make you a better photographer. That said, when I think about which camera created the most new possibilities for me, it was probably the rb67 pro sd. Prior to that, just about everything I'd used was small, fast, light. The rb caused me to prethink my compositions and become much more selective than I had been... with an F5 it was klick-klick-klick-whirrrr... end of roll. So the rb was a helpful experience for me. After that I realized that I could see what I wanted before framing it... a little epiphany. So then I took a step further to MF rangefinders, where I really felt (and still feel) very much at home. Now I like Amish boxes. YMMV.