Ignoring names and instead looking at the hardware, a 4090 uses 89% of the AD102 while a 1080ti used 93% of the GP102.Should you not be comparing the 1080ti to the 4090? Those are both nVidia flagship GPU's. So that is a £735 GPU vs a £1800 GPU. Even being generous and comparing the 1080ti to a 4080, that is still £735 vs £1080.
Taking inflation into account your £735 in 2017 would be £938 today. So for the price of the flagship GPU in 2017 you are getting an upper mid tier / lower high tier GPU.
People justifying the price rises in this way are what adds fuel to nVidia and AMD's fire.
A 4080 though has just 53% of the cuda of a full AD102 so the closest pascal card to that would be 1070 at 50% of the GP102 so your looking at a price increase of around 200% in 7 years, way above inflation.