UE4 has a lot of implementations (same as Unity) that can be harnessed by a developer. If a studio starts combining all these features, you get (IMO) a demanding game.
That does not change the fact that UE4 has an overhead and my belief that Hellblade could perform better than it does. At some point engines start compromising performance for ease of use and Unity does that far more visibly than any other multiplatform engine. Yes developers can harness it to the best but that's not to say those same developers couldn't have harnessed even more if they had the time and resources to get their game up and running on another engine.
What is 'better tech'? All of these games use similar tech (i.e. SSR is just SSR. Baked GI is just a popular method of getting a good ambient lighting + environment lighting for example); some may focus on one aspect of the tech and neglect another aspect of it.
It's funny you'd say that when your original post implies how this is a demanding game because of its tech. I've seen games that are more technically complex run better. A game that has the same amount of tech deployed but in a larger scale for instance is also more technically complex. I admit it's a vague term but as good as Hellblade looks I won't put it among the most technically accomplished tittles out there. It's around the top...but not at the top.
As for tech being all the same. Yes SSR is SSR but there is a varying level of implementation and precision across all the games. Look at Destiny for example, it has SSR and you'd think it'd behave like SSR in all games. But it doesn't, it doesn't get applied to every surface with a reflective property and is only seen on water bodies, which is not how SSR works usually as it's a technique that gets applied based on a surface's specularity rather than be selective about which reflective body gets it. It also ends up reflecting wrong as sometimes it can reflect the ground in front of the water body. It doesn't behave like SSR yet at other times it still behaves like SSR. And that's just an extreme example, point being despite the homogeneous nature of rendering technology they are not all the same and differences comes down in implementation and precision.
Which is where a game becomes a game with "better tech" for me.