I didn't even attempt the Hard path because after the previous Dragon Rescue where we needed specific dragons to progress. On those I spent gems rushing the last few key quests to get myself the needed keys, and then couldn't proceed because of the cooldown on the one specific dragon I needed. I wasn't going to do that again so I skipped it.
The annoying part of an event like this is that it pulls gems/money out of you early to get one thing, thinking that's all you'll need to get. Then you learn progressively about the other things you need. It takes advantage of the sunk cost fallacy to make players keep pushing out gems/money to get the next piece of it. Since they already spent 900 gems on the dragons they needed and 500 to get the orbs to empower them, because it's not clear if they need to be empowered or not, and then 250 more rushing all the quests to get the keys. If the game had just said it's 1650 gems to get the keys and all the dragons at the beginning, nobody would have done it.