Rewards does't justify the repetitive event. 700 gems could be given in a different, non-repetitive, event. Maybe an event that doesn't force you to duel standard duelists.
why do people complains so much about Duel-A-Thon event, it is free gems like 1000 or more in total and you fill up the meter ranking up in PvP and getting your cumulative wins for tickets
Every event force you to duel standard duelist.
Unlock event : duel standard duelist to collect items
Duelist chronicles: duel standard duelist to collect dice
Roaming event: duel standard duelist to make LD appear more often