The engine is more than 4 years old lol. You can slap a new coat a paint and duct tape the broken pieces together, but at heart its still the same engine Oblivion used.

You really think Fallout 4 is as good looking as The Witcher 3? It runs on a slightly modified 4 year old engine (or older if you count the Creation Engine basically being a modified Gamebryo Engine)... the games visuals are hardly impressive.