@ZachiasDenson
I think as other people have said on other threads, the speed guarantee is to your Hub. That would make sense, because beyond that, it's hard for BT to guarantee anything, as you own all of the equipment and infrastructure after the Hub, which is all massively variable.
It seems fairly likely that the 300 mbps you are getting over wifi is you hitting the limits of your wifi. On Wifi 5 devices, the best you can really hope for is 450-480 mbps in fairly ideal conditions. If you are in the 300 mbps range over wifi 5, then that's quite normal. Wifi 6 will give you faster speeds, but only if the router/mesh is Wifi 6 AND your devices are Wifi 6. None of the devices you have listed support wifi 6.
As for your wired tests, as you are getting 100 mbps, as @imjolly said, it sounds like your ethernet card is not gigabit. Your old laptop is probably old enough to be from a time before gigabit was the standard for laptop ethernet cards. You can solve that by buying a USB 3 to gigabit ethernet adaptor. Make sure it is USB 3.
Until you can properly test via wired ethernet on a gigabit enabled interface, none of the tests you are doing or will do are going to get anywhere near the 900 mbps you are hoping for. Once you have a proper gigabit test environment in place, if your speed tests are pegged at 300 mbps over ethernet, then you may be on the wrong package.
