By default almost all WiFi access points transmit at full power (100mW). This gives maximum coverage and users see a good signal (“full bars”). However, there are good reasons to turn down the transmit power to a fraction of the maximum.
The regulatory bodies are now strict about DFS requirements on WiFi access points. This applies to both new devices and updates to old ones. A simple firmware update may cause a lengthy delay before the network is operable.
The original Wi-Fi (also known as 802.11) used the 2.4GHz band. It is still the more popular band since virtually all devices support it. That makes it more crowded and it is also more prone to interference than the alternative 5GHz band.