Yeah, possibly. It depends on the industry. Like you couldn't directly compare Intel to ARM because their strategic groups are too divergent, even though they ostensibly do the same thing.
But within the same strategic groupings, it might become more appropriate to say "outsourcing or more/less integration is/isn't a good choice for this industry due to xyz". So at some point you might expect to see (for example) the manufacturer who mines their own metal's revenue to increase if there's ever a global shortage, compared to competitors who rely on other companies. So as in, the mining car company might have lower production numbers per employee than competitors due to a larger staff, but if vertical integration makes sense in that industry, you'd expect revenue per employee to demonstrate that over time.
In this case, if Tesla have lower production numbers per staff due to less outsourcing then that's just necessity, due to the fact that it's a tentative young company which sells a highly niche product. It'll work out over time if they can establish themselves in the industry.
But basically yeah you're correct, it doesn't make sense to look at a single metric in isolation, without taking a wider view.