I can agree tasks are annoying, even more as a developer.
No matter what I work on, tasks are expected and a lot of people get angry/sad if there's no task available.
I've tried around some with it, and it seems the most acceptable task system gives you exp and money rather than a item, if they give an item they better give exp as well.
on a 8.0 server some years ago, I had tasks there you finished a task, and you had to find a boss and kill it, and the task reset and you could repeat it, and the boss gave random exp/loot.
And all tasks was enabled at all times, so you could go dragons and collect 10 kills, and then go another creature for a while and come back doing dragons.
in my mind, I thought such system with all tasks enabled at all times would be appreciated by the reason you stated, people wont be stuck with 1 monster (and maybe there's no empty spots with those creatures).
But no, it was not acceptable, it must be 1 task, preferred 2 that you can enable, but not more.
And it shouldn't lead to bosses, you should get go to an NPC and claim your reward.
So the original idea with task, is pretty much gone as the community expect them to be all about exp/cash.