FritzBox 4040 slow 2.4 Ghz Wifi - should I try alternative driver?

The 2.5 Ghz Wifi on my FritzBox 4040 router is very slow (DL: 20-30 Mbit/s) in comparison to the 5 Ghz Wifi (200-250 Mbit/s). I've got a 250/50 Mbit/s connection. I was wondering ist this a driver problem? If so, could I try to use this driver instead?
If so, how do I do it? Download the original image, albeit without the original driver (ath10k-firmware-qca4019-ct) and with the new driver instead, and flash it through Lucy?
Thanks a lot for your advice!