It's quite difficult to argue about tactics and strategy without a specific situation and task.
So, what's the problem? Just upload a save file with one of those tasks, and we'll see...
But don't forget that the goal is not to collect more artifacts, but to defeat the enemy (although collecting artifacts also helps with that).
Well, it depends on the victory conditions. I don't think I need to tell you that I've won scenarios many times without even seeing the enemy's main hero... :)
Defeating the main hero (no matter how) is already half the battle. Moreover, the method I suggested is used against very strong enemies that simply cannot be defeated on the battlefield. And this plan is implemented quite quickly.
How quickly? The goal is to wait and eliminate the main hero from the enemy's forces, and then quickly run through the "remaining" ones? Is that what you mean? - I don't see the point at all! I just find him and eliminate him; that's all that works for me ;) - only in this case can we talk about the speed of completing the map.
In my understanding, medium-level heroes don't focus on collecting; they defend the areas that haven't been captured yet. And, of course, they collect from those with only one harpy:D
Well, my medium-level heroes are comparable to those with one harpy; usually, these are the enemy heroes and one of mine.
Just for fun, take a look at my map uploaded on this site. There are plenty of enemies to fight there;)
I'll take a look, but then be prepared to hear some criticism :D