XPS 8930 Tower Special Edition, Sk Hynix PC401 M.2 256GB PCLe x4 + 2TB HDD

Regarding the XPS (most likely a 2017 model), purchased on the Dell site in March 2018 :

The newer device interface spec - NMVe was designed specifically for SSDs which supports a range of more things what weren’t possible with AHCI. Although it always isn’t the case, some are still AHCI, and since AHCI was designed initially for spinning platters, therefore doesn't it logically follow that NVMe PCLe SSD’s would also mean they’re not designed for AHCI?

A list of questions have to do with the Hardware and the factory configured RAID setup in the BIOS based on 1 and 2 below:
1.) When reading the Original System Configuration on the Dell support site for this system, the description of the SSD reads PCLe x4 but no mention of NVMe. Searching more information on the SSD, I came across this picture Hopefully, the pic is visable on this platform where the description matches the Dell P/N as found in the Original System Configuration: (Dell P/N R2RPG)

2.) When reading the XPS 8930 Service Manual and the System board components, slot 8 (page 18) states : solid state drive slot (M.2 SSD).
The factory installed M.2 SSD on the XPS is used as the boot drive by Win 10. As far as the Dell factory configuring the BIOS in RAID with the PCIe SSD on the motherboard, this would be the most undesirable of the two options -either RAID or AHCI. Considering this is the standard configuration option during purchase, the SSD would be plugged in an M.2 slot as shown on page 12, in the service manual here). It wouldn’t be installed in a drive bay nor directly connected to a SATA port on the MB either. To further support this is the standard hardware configuration, if I had successfully been able to set up and create a RAID volume, I’m not seeing how Windows would have ever been able to boot because it would've needed to look for another drive in a RAID array that doesn’t exist.

A) Can someone clarify if my logic is wrong if it can't be concluded the 256GB SSD is being used as a cache drive by Windows and treated as part of the 2TB HDD?
When Windows 10 was initially set up from the OOBE, the IRST Dell driver package was installed from the Dell server (along with all other Dell drivers). And since I never accessed the RAID controller set up in either UEFI or through the Intel IRST user interface, no RAID volume was set up or even exists.

B). Can someone add more depth to the BIOS controller for these two drives ?  I'm not seeing any benefit with the current RAID setting and I don't plan to create a RAID array nor do I want to purchase any additional storage drives. Which brings to mind – NVMe mentioned at the beginning. Assuming the SSD is NMVe PCle, would that also mean it is not designed with using AHCI protocol if the SATA controller in BIOS were changed from RAID to AHCI?

C.) Are there benefits to keeping the RST driver installed after the change to AHCI? If there are, would it not be best to have installed the generic Intel RST driver as opposed to the Dell driver? And if so, how would attempting to uninstall the Dell Rapid Storage Technology affect the system ? 

Note: An attempt to change the SATA controller in BIOS triggers the following message:

BIOS message that appears when selecting AHCI

I'm aware of the steps to change from RAID to AHCI which involves setting the system up to boot in safe mode before botting into BIOS to make the change to AHCI.