"A bad workman blames his tools"
A good workman, however, creates masterpieces with what he's got.
Game engines are just middleware. How good a game looks actually depends more on the level design and art development than the game engine.
Engines only provide a set of tools. They may help in ease of implementing those tools but in the end it depends on developers on how well they utilize them. I feel that with the current generation, most of the top engines are more or less in the same page in terms of technical capabilities.
A classic example is how the last generation of games were created. We can all agree that Cryengine or Frostbyte or idTech5 may have had more "better looking" visuals than Unreal Engine but look at the number of games other than the flagship titles that implemented them.
UE on the other hand spawned not only games but entire franchises with varying levels of graphical fidelity and gameplay. I'm talking about Bioshock, Mass Effect, Borderlands and many more. These games used "a heavily modified" unreal engine and not just plain vanilla unreal engine. Which brings me to my "good workman" argument.
tl;dr :- no engine is better than the other in terms of graphics, it all depends on game developers