Was rather shocked to find BT hubs don’t allow you to change DNS servers anymore and force you to use their own ones, so I can’t properly setup adguard.
What routers are people using now that are reliable and will let me control my own network configuration
That’s depend on how deep you want to go with router customization. Most casual enthusiasts would do fine using an Asus router. Out of the box, the firmware is based on an opensource firmware (Tomato) and has a lot of features and options compared to their competitors. Feature-wise, it already blows other consumer-grade routers out of water. And because the firmware’s source is available, third-party firmware (asuswrt-merlin) is thriving and can be flashed with zero risk while adding a whole bunch of new features and customization options.
If you want something more, then your only options are using enterprise-grade routers (e.g. mikrotik, ubiquity, etc). Just note that these enterprise gears usually don’t have latest WiFi tech (or even WiFi at all!), so you’ll still need to buy another wifi access point and hook them downsteam of the router.