2.4 GHz is unreliable for me these days due to interference from bluetooth headphones and hearing aids that other people are using. The issues tend to only show up during extended periods of video streaming, and having looked at a bunch of traffic captures over the holidays, it seems to be limited to certain streaming services sending very large bursts of traffic at extremely high rates (likely from servers with 100+ Gbps interfaces using TSO to reduce CPU usage). That makes me think that the regularly paced bluetooth interference from real time audio streams limits the maximum viable burst size of a 2.4 GHz wifi radio.

Yes, this happened a bunch more over the Christmas holiday when we had an extra 3 or 4 younger family members all listening to music and videos over their bluetooth ear buds and headphones, which made it much easier to track down as it was quite a rare intermittent failure with only a single bluetooth device being active.

I have at least 10 neighbours on each 2.4GHz channel.

This also only works if you're not living in an apartment building. Even then, there's Bluetooth and other things that don't share spectrum nicely with 802.11.

Having lots of lower powered routers is actually better for interference.

MacOS won't roam properly unless the signal from the connected AP drops below -75db, so cranking the power on all your APs will give you worse performance if you move around.

Since most devices these days only transmit as strongly as they need to, this is actually great for spectrum sharing.