I think it's a good idea, but i think there should be some adjustments. I understand the develepors concern about having High lvl Giants and Elementels wandering the world. But it could done this way:
Just there should be lands where the high lvl monsters are, just like the sssilistra for dragons. Also an option is to put low levels, like lesser giants and elementels in normal areas like The Wold, Talos and Thikken Dal as region bosses or normal foes but is small numbers.
They should completly hostile, untameble for players and NPC's. That could make it work.