In fairness I'm not in the situation whereby I have to rely on many smart bulbs, so don't face congested frequencies. At last count though, we had 50+ WiFi enabled devices and we're yet to struggle on a BT mesh with router turned off. The archer and bt routers preceding it didn't have any issues either on solely 2.4GHz and mixed with 5GHz later on. Most smart home devices are 2.4GHz in my anecdotal experience. I do wonder where - if at all - someone has too many WiFi smart devices for their home router and it's causing real issues. For us, we buy smart light switches, as we have a new build with neutral wires in the light sockets. So a kitchen with 14 GU10 bulbs or bedroom with 8 GU10 bulbs can be served with a single Sonoff smart switch to each room for £10-£15 each. Lucky for me I suppose! No dimming, temp or colour control, but I think most likely, people who benefit the most are niche and possibly not using those feature sets all the time. If a standard ZigBee protocol can be developed that serves a multitude of devices, sure, I'll sign up if needed. But right now, it's a bit more miss than hit and people stick to a single ecosystem, whether that's Philips or otherwise for combined feature sets etc.
Most people call their internet connection "WiFi" and wouldn't know an IP address from a subnet mask. More than a couple have their routers behind their TV and complain their "Internet is slow". If they're short on physical ethernet ports, they can pick up a switch for £7 on Amazon or get metal gigabit one from Asda for £15. More devices using a wifi channel, the slower that wifi channel is for all devices. A slight oversimplification, but a generally accurate one. People aren't using Wi-Fi 6 smart bulbs. Most are 802.11ac at best. Zigbee is a superior choice generally for bulbs from every perspective. They aren't on the same channel as your WiFi (when configured correctly), they use less power (both in a wattage and decibel sense), they mesh effectively (which works brilliantly). We've got about 20 smart bulbs in the house, and 20+ other directly IP-connected devices. Could we have used all WiFi bulbs? Yes. Would it have been a sensible choice? No. Should most people use WiFi bulbs if they're putting in more than a handful bulbs? Generally no.
I've expired this, don't want to help them generate sales. Within 6-7 hours, the price hiked gradually from £18.50 to £24, this is a joke. The price was £18.50 since days ago. At every hour after I've posted this, they put the price up more or less by £1. May still be an OK price, but I don't like these practices, they did the same with the 2 pack E27.
They're fine for in excess of 100+ devices wirelessly in plenty of standard routers. You'll still have plenty of traffic going to/from the router from mobile devices etc via the hub. Find me a house with 150+ WiFi devices running simultaneously being the norm. Then find me an example of where a hub solves this instantly. Hardly any homes have that many devices. Those that do will provision for it. Most people would rather one of the four ports on their ISP provided router weren't consumed.
Now you're really showing your ignorance, it's the huge amount of extra traffic through the router that affects it, not what's in the airwaves, and many consumer grade routers just can't cope with a very large number of devices.