I think you have forgetten how much weaker the pound has gotten when compared to a few years ago.
The pound was worth $1.62 in September 2014 when you bought your Core i7 5820K:
https://www.poundsterlinglive.com/b...ound-to-us-dollar-exchange-rate-on-2014-09-30
Its worth $1.40 in todays money. So when you bought that Intel setup the pound was worth 16% more in value.
Hexus puts the Core i7 5820K at $389(excluding VAT)during launch:
http://hexus.net/tech/reviews/cpu/76649-intel-core-i7-5930k-22nm-haswell/
Now how much was the Ryzen 5 1600 RRP?? $219 dollars.
Lets now consider the Ryzen 5 1600 has a decentish stock cooler and the Core i7 5820K has none,so more cost. Basically a Ryzen 5 1600,motherboard,cooler,RX570 4GB and RAM cost less than what you paid for your Core i7 based rig when it launched and the pound was EVEN WEAKER at the time at around $1.25 which was a massive 30% more in 2014. I know because I helped out with some builds last year.
Then the need for 4 DIMM matched sets,and OFC the X99 motherboards were over £150.
Before all the silliness with RAM,I remember doing a new Ryzen 5 1600 including a B350 motherboard for £290,ie,the price of your Core i7 5820K alone,when the pound was 30% stronger and with no cooler.
Plus you have forgotten how expensive CPUs like the Core i7 5960X and Core i7 6900K were otherwise you probably would have not changed platforms.