> There's no such thing as the "Proper Solution", there's only the best solution we are able to come up given the current knowledge and circumstances

I think that is the definition of a "Proper Solution".

Another way to define a "Proper Solution" is: the fastest solution that still manages to be maintainable while meeting all of the requirements for the project which is not "over-engineered".

I think that's the broad-spectrum "proper solution". I don't think there is any application that wouldn't want to meet these requirements.