Misunderstanding 1: The inability to focus at small apertures is nothing to do with amount of light. You still have a lot of light with f/8 in sunny day, much more than at f/2.8 indoors. It is actually related to Phase Detection AF mechanism which operates much like range finder comparing images from different angles to determine it’s in-focus or not. Small lens aperture just blocks light paths from different angles, and as the result, makes AF sensor unable to work reliably or not at all.
Misunderstanding 2: Older Nikon cameras may not auto-focus reliably with a lens having a maximum aperture smaller than f/5.6. That may sound bad, if you assume that it means the camera will not auto-focus reliably when the aperture is closed down to f/5.6. That is not what Nikon is saying! Instead they are telling us that auto-focus may not work reliably on older Nikon cameras with a lens having a maximum aperture of f/5.6, with the emphasis on the word maximum.
As expected, the latest generation Sony RX100 V obviously does have much richer feature-set and specifications compared to its predecessors. It has a superior Stacked CMOS sensor with excellent image quality that surpasses all the previous generation RX100 cameras, faster Bionz X processor with a front-end LSI capable of handling up to 24 fps shooting speed, 315 phase-detection autofocus points, 4K video recording at up to 30 fps and very respectable slow motion video recording capability up to 960 fps. It can handle shutter speeds of up to 1/32000 sec, has a very nice 2.36M electronic viewfinder (EVF), incredibly fast autofocus and a few other nice extras, such as anti distortion shutter and ability to set minimum shutter speed when shooting with Auto ISO enabled.