In my experience this has not been true at all now that most Logitech mice use LE ("Bluetooth Smart") rather than BT. The only advantage the RF dongle has is that it works without an OS.... or on an OS without a BT/LE stack, like here.
Not really, Logitech actually uses the LE PHY even for their "RF" protocol, at least since the Logitech Bolt controller which is what TFA is talking about. You can sniff Bolt traffic with a LE sniffer.
> The minimum latency of BLE is 7.5ms (fastest connection interval in the spec) while ESB can be in the 100s of microseconds
This makes for an average 4ms of latency, which matches what Logitech advertises. Then USB is then going to introduce 5-10ms at the very least...
One exception to the "no BT/LE stack" case is the combo of Apple input devices paired with Macs or hackintoshed generic PCs with a handful of Broadcom-based BT chipsets used by Macs. macOS flips some bit on those cards that tells them to keep Apple peripherals paired at all times, which allows you to type and mouse around in the pre-boot environment and subsequently-booted OSes without drivers even on old BIOS-based machines which can't load EFI drivers.
Never seen anything for BLE; my wild guess is that Apple now simply puts a BT stack on their UEFI. Not too far-fetched.
But it doesn't really help the noOS use case, since you still need a BT stack with UI _somewhere_ in order to pair your keyboard for the first time.