I think the only thing I would say to this is, it doesn't really make sense to me that attempting a floor of the tower and failing doesn't consume a key. In every other activity in the game, if you attempt it and fail, the resource is consumed right? I don't keep my energy if the Dragon kills me, I don't keep my token if I lose my pvp battle.
Why does attempting a tower floor and dying not consume a key? That would make it exactly the same as all the other activities in the game, and completely nullify this roadblock.
Unrelated note, while I appreciate the "this is an advanced quest, you have to be advanced to do it" argument, and it isn't wrong, it rings a little false when the "advanced quests" are a set of 10 quests, 9 of which you can do easily by 1 - 2 weeks in, and one you cannot complete until potentially months into the game. That....doesn't seem well designed to me. But it would be moot if the keys just worked like literally every other resource in the game, so I accept the premise that only advanced players, by whatever subjective standard any reader considers "advanced" to be, should be able to complete the advanced quests.