I think that currently, the event is too short. I was done in about 15 min.
The rewards are nice, but the event is a little underwhelming in like excitement and stuff. Maybe make it so you keep going forever?
As in, you can keep battleing till ur outta shinobi and getting small rewards every 3-5 battles after the first 5 battles.
Considering this is a biweekly event, rarer than Kurama attack and Sage World Battle Fields, it should in my opinion, take more than 1/3d of their times.
It happens as often Great Ninja War, but with inferior rewards as well as inferior playability length.
It was a really fun event, and I enjoyed it while it lasted, just wi* lasted longer.