Even if you had 2 BT lines to your house they wouldn't be identical. Even the physical location of a pair within a multi-pair cable can make a huge difference. Every line is unique, you can't compare apples and oranges.
It’s really hard to answer that but I game fine on a VDSL line using a HG612 modem and a number of routers aimed at controlling latency for better networking.
normally it’s the isp equipment that offers very little help to refine your network and a base pin means little if your network is the core of the latency and packet loss.
So for example I have a modest 55 down and a 13 up. My base ping is around 6ms. If I run PingPlotter and I’m using a Ubiquiti Dream Machine at the moment and turn off the QoS I get packet loss and spikes into and above 150ms. I turn on the QoS which is FQ Codel based, I limit the connection by 20% on both down and up and then test again my highest latency is just 8ms.
so I would strongly consider looking into another router to control your network as the chances are it’s your equipment rather than the line that’s the issue. If you change your isp the issues will follow you till you start looking at your own network.
So you are still dropping packets and seeing an increase in latency with the edge?
Install PingPlotter and test, don’t go by the sites that offer test like DSLreports but watch carefully using PingPlotter.
Record when you see the spikes or packet loss and see what was occurring on your network at that time ie was someone streaming or downloading or a video call.
Make sure the QoS is working as intended on the edge. I’ve noticed a bug on mine which has remained regardless of firmware or resets where altering the network channels causes the QoS on the upload to set at a different rate than my input. A reboot is required to correct this.
Try PingPlotter and see how you get on, if you saturate your connection and see dropped packets look at the graph to see it’s from your network.
Also look at your modem, I recently tried the Vigor 166 out and that created no end of latency so double check your modem as well.