I am not yet on any WiFi6 Routers/APs (still on a mix of AC 2100/1900), but the biggest improvement I saw was when I transitioned to simply an arrangement of a main router plus physically distributed APs (routers in AP mode) around the house/property, specifically not anything involving mesh or AP range extenders, but instead wired ethernet backhauls connecting between main router and APs.
I figured it was best for my situation to try to connect as many as possible of our devices by wired, so as to reserve as much as possible of the wireless from the router/APs for truly the devices that only had the option or practicality of connecting wirelessly. We have well over 25 devices connected to the local home subnet at any point in time, a collection of phones, tablets, laptops, printer(s), Google Alexas, SmartPlugs, FireStick, and a common share server point for files, videos/pics, music, etc. Also, an old router in AP mode wired almost at the limit of cat5 distance in the backyard for exterior WiFi coverage back there.
It all works pretty good for local subnet traffic, capacity and stability for our purposes. Now, we are not heavy power internet users, regardless of the amount of internal subnet traffic banging around between the router and APs at any point in time. We are crappy rural ISP often not exceeding 5Mbps (yes, you heard that right). So, someone doing very extensive internet streaming or usage might not be inclined to consider my arrangement. Regardless, it is already setup to be able to best support an even broader connection to the internet.
I figure I'll eventually transition to the latest greatest WiFi6 Routers/APs at some point in time, but for now my arrangement works quite well with a generation back from lastest/greatest most expensive.