i suppose you didn't notice that this time the top reward does not require 3500 but only 2500 and this is blatantly the reason why the event was 'nerfed' this time on the ninja fragments side (while is not at all on the myoboku grasps, mood scrolls, seal scrolls side).

don't look at it with the perspective of the early f2p that plays since less than 6 months. On the late game is exactly what you need to do: hoarding 25-30k coupons and go in an event like this one that boosts a lot your power while granting you a rare ninja you want.

if you want it for the 'power boost' side then the event was not nerfed at all, you still get the same exact quantity of myoboku grasps, medium refinements and mood scrolls, the only part that was nerfed was the chance to get ninja fragments (but beware that hokage minato is actually more expensive than shisui...)