ISP provided routers are chosen for a balance between being cheap and being good enough that the common consumer don’t complain and need support.

This means that your router would probably not support the latest WiFi specification and the latest throughput enhancing technologies. This means that the ISP provided router could easily be your bottleneck if your connection is faster than 100 Mbps and you are only using it wirelessly.

For most consumers this is good enough. For most of the remaining customers it is good enough provided they put their gaming rig and smart tv on a cabled connection to the router.

For the last minority of a minority, consisting mainly of professional IT professionals, professional network equipment not chosen due to low price is needed.