For Iruka its *right way to get him for free, but Naruto...well I haven't done the math, but if I had to take a guess it'd take even longer to him even 3 star that way than getting king of hell from summon redeem store.

You can make the refine slightly "better" by mapping out what ninjas you get in survival, like the sound 4, Gai, Kurenai etc, then 5 staring those. Could also 5 star the survival redeem store ones. if you really feel like grinding elites you could also do the basic ninjas like Naruto, Sasuke, Sakura, Ino, Shikamaru, Kiba, Choji, etc.

That way, unless you save frags for eventual skill books for said ninjas, almost every single frag you will get from treasure/survival/weekend chase/blackmarket/redeem will go into refine points.