Different techs.
The main difference is in the way they store the scene in voxels. If you just have a big 3d texture even 8GB wouldn't be enough to store the whole scene, even though most of that texture would be empty data.
UE4 solved this by using an octree. The problem is that the octree is very expansive to maintain (I think it's a task better suited to a cpu, which might benefit the SoC architecture of consoles, while on Pc there would be lots of copying involved). They are probably (didn't read any pdf yet) solving this by using tiled resources, so only relevant voxel data is actually stored on memory. So there's no cost to maintaining the octree anymore.
The downside is that without the octree (which makes searching more efficient) probably the actual cone tracing becomes more expansive, but dunno if that's why the game seems to take place in a confined area or that's an artistic/design choice.
Long story short the ACE's just made the PS4 1.84 TFLOP GPU render like a 2.3 TFLOP GPU & there is still some empty spaces left to fill in to get even more out of it.
That's a silly conclusion. The only reason why there's empty spaces in the first place is because there are idle execution units, which means ultimately they are not bound completely by processing power.
That's just words however. If every other system packing a GPU does not use theirs equally well one might just as well say the PS4 is 'punching above its weight'.
That would be true if only the Ps4 gpu among all the gpus on the market had "something" that enables more efficient usage, but that's not the case.
It tends to be bounded based on how much you have going on at a given time.
Like that's part of why Deep Down happens in caves.
Looking here, while you see a long ways into the distance, there's not much out there.
It's a really nice solution if you don't have a technical requirement that would cause it to be more problematic though.
For Epic, a lot of people would want to use the engine to make an open world game with a lot of stuff on screen, and a lot of it might be moving (like foliage), so they switched to a baked lighting component.
Lionhead has Light Propogation Values added to the engine which don't look as good, but can work better in a large, heavily dynamic environment. It's the solution Crytek pioneered.
Lionhead took a step further though, instead of working on screen space they are also using a voxel representation of the scene, which allows them to simulate more bounces, have emissive materials, and have objects not on screen interfering on the lighting. IIRC they can also use the voxels for a glossy reflections.
