It's an IoT device, not a laptop. It does not really need 5ghz to fulfill its purpose as an embedded CPU, and adding 5ghz likely would require making some room for it by removing other functionality.
So, I was measuring about 250KBit/s on an ESP32, and I decided to test everything that might increase the speed. I tried all the available antenna options for the ESP32 including many exotic antennas using the IPEX antenna connector variant of the ESP32, the stock ESP32 pcb antenna, and several chip antennas. A couple of them got up to 300KBit/s.
I also decided to see what happens when I power everything else off except for a single wifi router. So I did that, and I found that the stock ESP32 pcb antenna still got only 250KBit/s, and the other antennas measured exactly the same as they did before shutting everything down, too.
So, I don't know... 2.4ghz seems fine to me from my anecdotal tests.