I’ve also experienced some problems with connection reliability, but only on longer runs of about 100m or more.
You can connect a wireless access point to the powerline bridge. Using a different SSID and channel for each AP will always work. Also, some APs can do “roaming” between APs configured on different channels, but with the same SSID. You have to pay a lot for that, though (at least a “small business” -class device), and then also make sure all APs are a uniform type. In either case, the presence of a powerline bridge won’t make any difference to the access points.
So for many people, they not only still need a modem, but also a router, and then these access points. Or they just rent the giant piece of shit Comcast modem for $10 a month that has everything in one (giant piece of shit) box.
I’ve set up apartment buildings and libraries with Wifi. Ubiquiti is too complex for the layperson, and Meraki is now your typical overpriced Cisco gear with annual costs. Open-Mesh is cheaper and very simple to set up (step one, mount on wall; step 2, plug it in and it connects to the mesh. Done).
