The only truth in these advertised speeds, is you may briefly get them when doing a hardwired speedtest.
ISP´s can see a speed test when you do it and ping back a suitable response.
As a defining point of how good your internet is, the speed test is quite misleading as it gives you a point in time speed test for a few seconds and does not give you any more than a quick snapshot - no stability or ongoing reading.
This means you can have 300Mbps, one second, but the next it could drop off to 1Mbps, but the speedtest would say 300Mbps - useless!
As another poster has mentioned, in theory most households should not need more than 50Mbps - HD TV is 4-6Mbps, 4K is 15Mbps, so a couple of TV´s and a videogames console & PC should be fine all at the same time.
What the local suppliers are doing is the same as everyone else - selling you on the numbers. Which makes no difference.
My internet has not improved since i´ve gone from 200, to 300, to 600Mbps.
Occasionally it drops out and sometimes the speed dips as can see this on live measuring (continual tools).
To confuse matters further ISP´s can control the flow of data into any device separately - so you can do a speedtest on your laptop, but this may not reflect the speed of another device in another room. The ISP can monitor and throttle any connection.
With WiFi you never get the full speed, the further you go from the router, the weaker the signal, the slower the speed. Most even old devices should be sufficient in terms of reception speed, as you don´t need that much for the average user's needs. Where the differences may be is in terms of antenna reception performance or the size of.
Paul
www.televisiontechnology.eu