A few words ,
a prooer design determines the type structure , materials to be chosen , physical measurement , all these to withstand the forces , conditions for the part to do what it was designed for , an improper choise of the mentioned mean a less good of a job done by the designer .
So , be it a light metal skeleton covered by a suit of fiberglass shell for the scale appearance while doing what it was ment to do still could be a proper design , taking in consideration costs . Might be also manufactured from any other material that will have the sufficient characteristics to do just the same , again considering costs ... choosing a full metal and much heavier structure just because it looks nice is what I would call a poor design ..

same for any other part of the airframe ..
That is the difference between ....
looking at ; installed lights , bright shiny collors , is like judging the quality of a wine by observing the lable on the bottle...