In this case, the router used may be poor, and the performance is lower than the performance of the WiFi chip that comes with the fiber cat; It may also be a problem with the router configuration, such as the channel used by the router's wireless network is congested, the channel bandwidth is set up, or the router itself is faulty.
Under normal circumstances, the performance of the wireless chip of the middle and high-end router should be higher than the performance of the WiFi chip of the fiber cat. The specific model of the router and the fiber cat is not said here, and the performance level of the two devices cannot be judged.
Think router WiFi is a little faster, but there is a point from the gateway to the router to connect to the device 5G line.