These features are enabled by default in UE5, devs aren’t going out of their way to enable them. Epic lies about them being beneficial to performance, which is only true if your assets are shit. Nanite is especially bad because Unreal Engine doesn’t have a different approach for automatic LODs; you either need to do it all yourself or use nanite.
Not to say that devs aren’t to blame - they should know better - but they are just following Epic’s recommendations and defaults.
Real time global illumination (Lumen) and runtime LOD generation (Nanite) can’t be made much faster; it’s not really about optimization, it’s that these features are fundamentally slow. The problem is that Epic spent a shit-ton of R&D developing these, and they do save developers some time - at the expense of disk space and performance.