Personally i do love the feeling of joy when encountering the Area Boss (especially when u have a quest for it as well and even more when multiple players try to chase it)
But - would suggest having a NPC or a portal in the Area Boss map that will spawn a no exp no drops version of the boss for the kill quest, at least for the early bosses. probably a little hard to implement.
Anyway the balance here is not heavily gravitated towards these quests and you can level just as quickly in other places and catch up in the end (specifically the Mano one is goated though)