Raids are endgame content. They require coordination, communication, and team effort. In my opinion, each chest should drop an Enhancement Prism, and the final chest should drop an Ascendant Shard. Raids aren't even as farmable as Nightfalls, so I don't understand why they don't include raids as a path to these materials.
But that's just my opinion.
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Random drop chance from all chests would be a better idea and the chance increases per chest opened! This would deter the boss farm grind and promote doing the full raid if materials where needed. Would also feel more rewarding to do the full raid. Good idea all the same if reasonably done!