Regarding the creature types, Giant is interesting.
(I havent seen Bigby yet, so am unaware of anything new it mentions.)
There seems a continuum:
Primordial → Elementals → Storm Giant (Elemental Chaos?) → Elemental Giants (Fire, Frost, Cloud, Stone) → Hill Giant → Ogre → Orc → Human
The continuum is from completely inhuman and elemental to more and more Human until actually Human.
I dont know of any narrative that explains this phenomenon. But the Orc seems part of it.
Maybe the Goliath descends more directly from the Stone Giant, without a Hill Giant intermediary? But the Goliath too is part of this humanization process.
When I think of the Giant, I think of the jǫtnar and their animism. It is the mountain itself, the ocean itself, the air itself, the winds themselves, the fire itself, and so on. The Giant feels highly Elemental. The 4e Giant emphasizes the elementalism. I am glad to see 5e continue this.
I see the difference between an Elemental and a Giant as: the Giant is an Elemental who is native to the Material Plane.
The Elementals are far away in the Elemental Planes and feel more abstract. Instead of the Earth Elemental, the Giant is a specific rocky feature of a particular mountain within the natural wilderness landscape. Instead of the Fire Elemental, the Giant is thermal activity of a particular volcanic region, or of a baking desert wilderness. Instead of a Water Elemental, the Giant is the frost of a particular glacier. (Also the Giant can be a particular river, lake, or sea.) Where there is an Air Elemental, the Giant is a particular cloud, a particular seasonal wind pattern. And so on.
As an aspect of the Material Plane, there is some kind of affinity between the Giants and the Human going on.