Its not that bad. I ranked up in a Samui, Omoi, 3rd Raikage, Wind Main lineup and that took me about an hour or so (52k power). The Ninjas it gives are hit or miss. One time I got Jigokudo which helped me get him to 4 stars. Another time i got Cee frags. Maybe they could update it to GNW Treasure instead of Kage Treasure ninjas but either way, if you have even just a single good lineup for Arena, its just a matter of time before you get Six Paths.