None of us like a decline in so many things. However, I find it totally incredulous that anyone can be complaining so much about speeds above 70Mbps when more than half of my village is below 10Mbps and quite a few below 5Mbps
I was once on adsl and it sucks but they put it all down to how far you are from the cab or exchange in my case I live really close to my exchange less than 60 metres so when my line speed drops or declines
Your OP tells us you are about 150 metres from the exchange / cabinet!
Here we are about 60 metres from the cabinet and 200 metres from the exchange. We enjoy a rock-steady connection at all times.
At the moment, she who wears the trousers, is watching a streamed movie in another room while I type this. There are 3 iPhones, 3 iPads, a laptop and 2 desktops all connected. The BT Speedtest reports 74/19 which we have enjoyed for years. We have never seen 80 but sometimes the speed will drop to 65 or so but soon settles back to 74 once more. You wouldn't know there was anything untoward unless you actually performed a speed check.
The distance to the exchange is totally irrelevant, the fibre to your cabinet may not even come from your local exchange.