A 50 Mbps plan can serve 30 smart-home devices easily. What breaks first is the router's device table . Cheap routers cap at 30-50 simultaneous clients. Add 25 IoT devices, 4 phones, 3 laptops and a console and you'll start seeing devices fall off WiFi randomly.
Security cameras and doorbells stream upward to the cloud. Four 4K cameras recording continuously need 16 Mbps of upload. Cable users on slow upload tiers should switch cameras to motion-only recording.