2.4GHz wifi at 40MHz squats literally half of the usabke channels, you speed improvement, very likely you now get 100mbps. If you just disabled 2.4GHz and forced 5GHz you would get the exact same improvement and wouldn't be polluting half of the available frequencies.
Add another idiot sitting on channel 8 or 9 and the other half of the bandwidth is also polluted, now even your mediocre IoT devices that cannot be on 5GHz are going to struggle for signal and instead of the theoretical 70/70mbps you could get off a well placed 20MHz channel you are lucky to get 30.
Add another 4 people are you cannot make a FaceTime call without disabling wifi or forcing 5GHz
Add another idiot sitting on channel 8 or 9 and the other half of the bandwidth is also polluted, now even your mediocre IoT devices that cannot be on 5GHz are going to struggle for signal and instead of the theoretical 70/70mbps you could get off a well placed 20MHz channel you are lucky to get 30.
Add another 4 people are you cannot make a FaceTime call without disabling wifi or forcing 5GHz