I understand the high risk high reward but if I compare the time it cost to do for example 50 waves only to die after that and get zero rewards feels really bad to me.
Maybe give the chest rewards at certain thresholds like wave 25/50 or something to make it more worth it?
With the monolith quests it seems fine as you just drop some echoes but in arena it just feels bad?
The only thing you are losing by dying in Arena in higher levels is the Golden Arena Key, which is a bit unfortunate.
However I think the idea of not granting you any rewards, including the Golden Arena Key, after dying in Arena is defendable and does not have to be reworked.
I personally hate it when the game crashes in arena/monolith (not so much arena as I do that for the fast levels), losing because of bugs is frustrating.