One can often reverse engineer things. Doesn't mean the process is the same as the original. It's been proven scientifically race car drivers see differently than most. Who's to say a great artist doesn't as well? Second guessing hundreds of years later with a totally different outlook means little when the truth is lost to history. Maybe? maybe not. That simple.
Not sure if you saw it either, but to me the movie was a detective story, a cold case story.
It was basically a response to David Hockney's book about his opinion that painters have often had "help".
So it's just an opposing thesis to the common one that states Vermeer was a genius with light which I'm guessing you ascribe to.
The movies thesis is:
1. If Vermeer's work looks like a photograph mainly because of his gradation of light or exquisite transition from specular highlight to shadow mainly on faces and round objects and
2. his work was one of the only ones that were able to achieve that, why is that?
3. then maybe he used a technology to achieve that....
So Tim, the subject of the movie and a engineering type nerd sets out to try to figure it out. And in doing so reaches a conclusion to his thesis, and to try to prove his thesis, decides to paint a "Vermeer". And since he has no art or painting background, he starts from scratch and the movie follows his progress as he paints his "Vermeer".