Hi there!
I would not say, that it is not the right solution. It seems that the board you are using is not exactly the same as the board I used to develop the project, and it behaves differently when it comes to modifying the CPU frequency.
The ‘slowDownCpu’ function is used to slightly slow down the CPU and save energy, as it’s not at all necessary to run at the maximum speed the ESP board can offer. Removing this function will only result in your ESP board consuming a bit more energy, but it will likely be negligible.
Regards!