I'm copying the same reply I just posted in a similar topic:
Thank you for your feedback! We want to keep iterating on the exclusive Versus and Dungeon units, so all your comments are incredibly useful!
We're reducing the requirements of most of the Arena quests, and increased the time for completing the quests to 24 hours, with 6 minute cooldowns before getting a new quest. With these changes, we hope players are able to complete quests in a more relaxing and at a razonable pace.These changes will be up during the next Arena event, scheduled for Monday 14th.
Of course, if those fixes are still not fair enough, please let us know and we will keep improving them!