When you deconstruct the event to see what is the best chest choices for the grand prize as is done for every event it should come as no surprise that INNO took that information and used it against the players in stacking this events odds.
Look at the history of events
Phoenix 2020 -- Feathers / Grand Prize -- Light Wood (19), Red (84), Gold (53)
Elvarian Carnival -- Flags / Grand Prize -- Light Wood(18), Blue (30), Gold (54)
Autumn Zodiac 2019 -- Stardust/Grand Prizes -- Chests 18, 29, 85
Mermaids -- Pearls/Grand Prizes -- Clam (18), Cantharus (29), Yellow Prickly Cockle (85)
This event
Autumn Zodiac 2020 -- Grand Prize -- Golden Keys 139, Golden Keys 121
If that does not speak volumes to you as to how the event was rigged against you then I feel sorry for you.