Here's a perfect example:
This is Shenmue I, running on whatever Sega AM2 was using to develop it.
This is Shenmue III, running on UE4.
The difference is that the game that came out in 1998 had much more talented people working on it. People that had worked on Virtua Fighter, one of pioneers of good animation in 3D games. The other game was developed by a bunch of cheap labor, with no experience.
There is no question that UE4 is a much better game engine than whatever the first 2 Shenmues were running on, but the people that made the first two were much better at their jobs and had much more experience. A game engine is just a set of tool that make your life easier as a developer. If you're not very good then there's no set of tools that will change that.