Until you try to add / modify a feature of the software and run into confusing template or operator or other C++ specific errors and need to deconstruct a larger part of the code to find (if possible) out where it comes from and spend even more time trying to correct it.

C++ is the opposite of simplicity and clarity in code.

Yes, but they are still all hidden.

constexpr means running code at compile time. template means duplicating lots of code lots of times. these are not cheap.