See, I assumed something like that, and just like you mentioned with Win10 USBToGo, I assume some bad things will mess with you on Win7 USBToGo too, I’d not use it and setup a real Win7 install unless you have other options.
You can’t revive the Dell 
Or is it some physical issue. Win10 sucks, no good BIOS toy developer is going to validate anything for Win10 until they absolutely have to.
Do you think ASUS does block the chipID of the installed BIOS component << I don’t understand what you mean there? But in general, no Asus isn’t blocking any Chip ID’s, they don’t have anything to do with this.
And on the FPT discrepancy, it’s probably just FPT detection issue/thing, from the fparts.txt only having 5F instead of both 3F and 5F or just bugged detection in general. You looked at the chip yourself correct, and it’s 3F?
Try this, if still no luck then it’s a Win10 issue for sure. First, double check you have the chip in he correct slot, and installed in the correct direction, plug it in the USB and wait 10 seconds, then feel the chip itself, if it’s not burning your finger hot then it’s in correctly 
Then with ASProgrammer application select the chip from IC>>SPI menu (Macronix>> MX25L12873F) >> Then click read ID (two over from stop sign, right left of the icon with lock on it) - I guess it does have detect
YOu should get this
ID(9F): C22018
ID(90): C217
ID(AB): 17
ID(15): 0707
If so, or not, click the lock icon drop out menu, right left of stop sign. Then choose edit SReg, and in the box that comes up click Read SReg and show me image.
Then, on the lock icon right next to stop sign, click the main lock button (Unprotect). Then try to erase, blank check, open BIOS file, then write/verify.