I realize you were debunking the idea that Macs are more expensive than similar PCs, but there's a lot more behind those listed prices that differs other than the SSD size.
The Macbook Pro has non-removable SSD and RAM. SSDs are consumable items, and while the life they have is much longer than people think, it still makes the Macbook Pro a disposable computer that costs in excess of a thousand pounds. I wouldn't even consider such an item unless it was bargain-basement cheap, which the MBP is not.
As far as the RAM and SSD sizes, 8 and 256 are fine to start, but not if that's going to be the final tally. The smallest amount of SSD storage on any of my laptops is 1 TB, and that's feeling a bit cramped lately (thinking of upgrading again).
The bit about the RAM being soldered is an issue in the XPS 13 too, but in the x86 market, I have tons more choices with the same or very similar specs, and at the same or very similar price point. You don't get that with Apple.
Ifixit's most recent score for the Dell XPS 13 was 7 out of 10, while the most recent Macbook Pro 13 scored all of a 2. That may have changed, but for now, those are the most recent numbers. On top of that, you can get parts for a Dell, but Apple does all it can to make sure you can't get them for their products, and if you go aftermarket, they could release a firmware upgrade that breaks your expensive disposable device down the road. They've done it before, and even though that was on their other platform (iOS), it demonstrates that the company thinks bricking your hardware because you dared repair your product with unapproved parts (when they refuse to sell you the approved parts) is okay.
The new M1 is very impressive, but as long as it's only available in Apple machines, it's a whole lot less appealing. We will have to see how the other CPU makers respond. Super wide decode and execution unit architectures aren't in any way restricted to Apple, though I would not be surprised if they tried to claim otherwise, given their history of thinking they owned the entire market for any product they introduce, whether that be GUIs or smartphones in general or even the concept of rounded corners on a device that's to be carried in a pocket.