I don’t know why Crowns can be only found in PVP or explore but the choice has to be superficial.
Therefore I propose that crowns can be found every where Gnomes are during these Kingdom events.
As it stands we have to grind explore or PvP for crowns. Then grind quests for Legends Reborn. As for challenges? When they create a 25th hour for each day then you will have time for challenges.
The Xenith is not too scary, but I am not sure, if future legendary battlecrashers might be.
Better to keep them out of the arena, if you are asking me.