This is currently still a very arguable topic! You are right that max melding i170 tool is impractical and pretty much impossible. On that sense, i180 is so much more desirable since it is hassle-free and gil-free but with much more impressive stats than an unmelded i170. So why would someone still pick the i170? 2 reasons: (1) 4 extra CP and (2) faster gearing up of all 8 classes. Do not underestimate what some people can do with 4 extra CP. In the right hands, 4 CP can be magical!