>but still the spec literally hands you a schematic. Is it that hard to just copy it? Why did they even try to be clever and use their own design in the first place just to save a single 5.1k ohm resistor?

See also: People who like to get all creative with encryption library implementations in commercial settings. If implementing a standard protocol, unless you have a very good reason otherwise, you should;

1. Go and find the guide by the people who designed it.

2. Read the guide and make test thingies till you are sure you understand it.

3. Now go and do what the guide tells you to do.