Slow WiFi 2.4 GHz

Some month later, here is an update of my case: I’m running wifi only with 5ghz band now, because the 2.4 is not working fine as soon as the Bluetooth is on.
I own a smartwatch so there is always a bluetooth device connected to the phone…
When I’m using WiFi 2.4 I cannot get more than 3mbs
If I switch to 5 I’m at more than 30mbs at the same place.

Some tests:
Wifi2.4 + bluetooth on:

Wifi2.4 + bluetooth OFF

Wifi5 + bluetooth on

Very disappointed… How can the engineer missed this problem?
So I’m with 5ghz all the time, and sometime it’s not very convenient.’’