They are not worth it, the best ones are lvl 75 ones in Gaaraland and they give just over 10k exp. You need like 500~ bread to level ninja 1 to 80 so you would need 2.5k~ fights.
If you want to be efficient with exp just swap your ninjas while you sweep, daily sweeps give like 10m~ of free exp a day.
yeah i recently got like a ton new ones and the food just comes and goes especially with ranked team that needs to stay up to date. I was waiting this morning for arena and was killin some zetsu's in the meantime and doing sweeps just to keep busy but it got the lvl 1 nin to 30 quickly so helped a bit.
These world mobs really should give MC exp. What's the point of putting them there when they can be rendered completely obsolete by instances and food?
I won't even mind if they take that exp and divide it by 10 to give out as the MC exp.
Well a mod said something about that on another thread that I saw, that if you could just level like that, that peaple would be capped in no time. But yeah if you only get a tiny bit then it would take long too so you got a point there...