This was true for the first event. One of the players complained that there were fewer people playing than in the DMM version, so the devs obligingly reduced the rewards. I noticed the rewards were un-nerfed for the 2nd Dummykun battle, but kept quiet because who wants nerfed rewards? As this is a rematch of the 1st, it seems the rewards are still nerfed.

So - score in the top 500, or get below 1 upgrade in medals. I was 504 the first time, not that I'm bitter. I ranked just outside top 200 on the max damage version, but then the competition was less fierce - because they didn't nerf the rewards.

I'm around 450 so far, after 1 run with each team on non-optimised builds and with non-optimised friend's Eidolons. I'm going to have to go back and rerun basically every team to make sure I'm above the cut.