FWIW - I guess I’m a “power user” because my home currently hosts 307 devices, 109 of which are Zigbee devices. All connected to a ST V2 hub and all working just fine, thank you. And most of those Zigbee devices are battery powered end nodes, to boot!
As previously noted, the trick is to distribute enough A/C powered Zigbee devices that will act as repeaters throughout your property. For me, that means at least 1 Zigbee wall switch in every room, plus a few SmartThings SmartPlugs around the exterior perimeter of my house (to pick up the 26 Zigbee Spruce lawn moisture sensors scattered across my 2+ acre lot).
One other important consideration: you want to make sure that the Zigbee channel your Hub is using isn’t overlapped with another Zigee device (e.g. Hue) and/or your WiFi channels. Such overloaps could limit the number of devices you can (reliably) connect.
Since the Zigbee channel gets auto-selected by the hub at initial install, and cannot be changed later, you might have to install/remove your hub a couple of times until it selects an out-of-the-way Zigbee channel. My ST hub uses Zigbee Channel 24, my Hues use Zigbee 25, and my WiFi uses channels 3 and 8 (I have neighbors on 1/6/11). More info on Zigbee/Wifi overlaps is here: