I have some additional feedback about arena chests: The epic (purple), legendary (gold), and mythic (red) arena chests take way too long to open, and the rewards don't feel worth it for how long it takes. First 36 hours for the mythic chests is way too long to get like 4 cards. It's just silly. Likewise, 24 hours is very long, and even 12 hours feels ridiculous for a purple chest.
Worse, the pirate silver reward you get from the chest makes it a punishment to get high rarity chests during events. It should not feel like a bad thing to get rare chests, but if you're trying to maximize pirate silver, you're best off pulling common and uncommon chests (1 and 2 hour) from arena, since they reward the same proportional amount of silver per unit time. But the rarer the chest, the worse they are for your time and you actually lose out on silver because you got a rarer chest.
You ought to adjust the silver granted from chests so that they reward a proportional amount of silver per hour, and you should really decrease the amount of time you have to wait to open the very rare chests as well since they just take way too long to open. Essentially, at the moment each tier of chest only gives 25 more silver than the last, but takes something like twice as much to open, meaning each one is worse than the last for farming pirate silver during events.
common - 1h, 25 silver
uncommon - 2h, 50 silver
rare - 4h, 75 silver (should be 100 silver)
epic - 12h, 100 silver (should be 300 silver)