Why are you measuring frame time … when you’re not GPU limited … in the editor?
Like, sure, that’s probably something that affects you personally, but it has almost nothing at all to do with what real games will do with high density nature assets on shipping builds on target hardware.
Figure out what your hardware target, and available development time, is. Use any or all tools available to you to make the best game you can make for the given target hardware in the given development time budget. If Nanite is part of that, great! If Nanite is not part of that, also great! For gnarly outdoors scenes with typical 3D photogrammetry scanned high-realism assets, Nanite is absolutely a win for a large subset of the games using those techniques. If your game is somethign else, it might not be.