You said it, I completely agree with you. For me, I work at 1080p and use TSR, so my actual RT cost is low enough that I have some performance headroom. And I should clarify, do you mean standalone ray-tracing (SRT, just for ease of use), or Lumen RT? I have discovered you can make them look more comparable by letting SRT evaluate all material roughness, but the performance cost is absolutely not worth the (minor) visual improvement.
It’s not that cubemaps are necessarily bad (CryEngine’s Neon Noir raytracing demo used them for dull specular, because you practically can’t tell), but they are a PATA to author, configure in such a way that looks acceptable, and check that your materials will look good with them. Not to mention, they break with dynamic worlds, although I do know that some of Lumen’s multi-view capture tech was rolled into the new cubemap implementation, so I wonder if the performance has improved enough to allow for practical dynamic cubemaps.
And you’re totally right, modern PBR art pipelines already generate content that hides many of lumen’s shortcomings, but now that we have the chance to do so much more with Real-time lighting than we used to be able to, I don’t like the thought of a minor technical limitation holding back all that potential.
And thanks for the hack, I really appreciate it. I’ll float an idea: UE5_Main now supports mirror reflections on translucency (and I will say now, Lumen and PT are almost indistinguishable in most scenes), but 5.0 is stuck with their radiance probe projection trick, which does solve light leaking at least. I wonder if it’d be possible to have subsequent bounces of reflection to simply grab from the nearest radiance probe, it wouldn’t be excellent quality but it would certainly be better than returning black.