If you have non fibre broadband , then the service is delivered from the exchange, it’s a rate adaptive system, the longer the line the slower the service, so it follows the closer to the exchange the ‘faster’ the service, that is what the posted graph shows, it plots speed against distance...if someone lives closer to the exchange than you, but gets slower speed , that needs investigation, bearing in mind it is the length of the cable from the exchange , not an ‘as the crow flies’ distance
You haven’t actually posted what speed you should expect and what speed you get, perhaps you could as already stated post your router statistics and the results from a DSL checker like this
https://www.dslchecker.bt.com/
I appreciate that your enquiry is for more than just yourself, but if your details show that your service doesn’t need to be as bad as you state it is, then any fixes could potentially be applied across the board.
