Now that the event is over and rankings are released (I ended at 12th), I wanted to share my strategies which made me the first person to score 1 million points and placed me at rank 1 on the leaderboard for quite a while at the beginning of the event.
Rosa: I alternated Seed Bomb and Bullet Seed, hoping for as many flinches and speed/accuracy drops as possible. When my sync cooldown got to 2, I used two TMs. After that, I just spammed Seed Bomb and Sync until time ran out while hoping for misses/look alive procs.
Brendan: TM twice right away and Liquidation. Alternate Waterfall and Liquidation until first sync, making sure the last move before sync is Waterfall. After first sync, just spam Liquidation except again the last move before sync should be a Waterfall that gets a flinch to activate Interference Sync. Hope for early accuracy/speed drops, a whole lot of misses, and every 60% flinch and 80% sync crit.
Arven: The most boring one in terms of strategy and resetting for luck. Immediately body slam for para, then use five brutal swings for debuffs, then TM twice before Sync. After sync, just spam double edge. To get 300k, you need two full paras and of course every sync crit.