George wilbur expertise.

Yes, of course.

But the film-makers were more concerned with creating comedy and humor. Not so much "simulating" what a real-life court case would look like.

The method you described would be quite legally sound and quite realistic, yet quite unfunny. The last being the most critical in the eyes of the film's writers and producers.

Why would George Wilbur know minutia about 1964 Buick Skylarks and 1963 Pontiac Tempests? It was never said that he was a car expert; he was an expert in rubber analysis, or at least he knew how to operate a gas chromatograph machine.

It's not even particularly believable that Mona Lisa and Vinny knew all that stuff off the top of their heads, because that's the type of knowledge that comes from a lot of reading / research, not from simply being a mechanic. Well, anyone who knows cars knows that a car with a standard open differential couldn't have made those tire marks, but the other stuff, such as what year the Chevrolet 327 c.i. engine was introduced, what year it first appeared in a Bel Air, what the factory ignition timing was, and knowing what was and wasn't available for options on 1964 Buick Skylarks and 1963 Pontiac Tempests... that's not stuff you tend to pick up just from working on cars, i.e., that's not mechanical knowledge, that's Jeopardy-type trivia. I've known a lot of mechanics, and their knowledge of car trivia tends to be small, and what they think they know is often wrong. That doesn't mean they aren't good mechanics, it just means they don't do a lot of studying of topics that don't matter.

Using movie logic:

Lisa wanted him to win. George Wilbur was brought in by the prosecution. He knew that if he got Lisa on the stand and talking, then she would basically do an information dump and lay out all the facts about how she can tell that a Pontiac Tempest made the tracks and not a Skylar. Wilbur on the other hand would only say what he was required to say in order to answer the question, and nothing more. Getting him to come to the same conclusion as Mona Lisa did would have taken a lot more time and effort, and Vinny was running out of time before the judge busted him. It was just easier to have Lisa lay out all the facts, then ask Wilbur afterwards if he agreed.

Had George Wilbur had that knowledge he'd not have testified in the way he did. His report would have pointed out the inconsistencies between the evidence and the case as it was presented.