If you like small group PvP (2-4 players) and solo PvP check out my video https://youtube.com/watch?v=jechGImtFio
SPOILER: The first 40 seconds of the video contains a scene from the final Molag Bal boss fight!
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None of the above.
The only real way to fix this is make every dungeon boss like the 4-man dungeons; instanced to the player/group. If the boss is not instanced you run into problems with any choice made.
Nerf loot with timer, fight a boss, get no loot:
If people want to camp at a boss for loot they should be able to. They should not be punished because of botters. The instanced bosses will help with the bot problem because the bots won't be able to have 10 bots spam kill the boss in 2 seconds. Also increase the difficulty of the boss so a single bot can't just hold down the attack button without healing, etc to kill it.
Increase spawn time:
This actually wouldn't be a bad idea IF the instanced boss idea was implemented into the game, but if the bosses are still not instanced this would be awful. It is already bad enough waiting for a boss to spawn just to kill it to complete a dungeon/quest. It completely ruins immersion which is another reason dungeon bosses should be instanced...
Leave it as it was:
Obviously that wasn't working. If they leave it as it was they need to make the bosses instanced for the same reason I mentioned before and they need to increase their bot banning abilities.