Responding to your edit: It's ironic that your professor seems to have taken pains to rule out all of the framings that would render their assertion correct, in (I presume) an effort to try and come up with some sort of universal rule that works in any industry and any context.
I'm pretty sure it's due to exactly that sort of hubris that business school folks have invited so much disdain. The domain in which you're operating simply cannot be dismissed as an inconsequential detail.
Tangentially, there is a subset of law firms that do operate as if total hours worked is the only thing that matters. Over the past decade or so, they've been rapidly losing ground to law firms that, by not thinking that way, manage to do a better job of producing the kinds of output that clients actually want.
I can see why, my limited experience with white shoe law firms was they billed us 100 hours for the 10 minutes it took a legal secretary to do a search and replace on another contract they did for someone else.
To be fair to my professor, the question does make sense in the context of the subject. That is, the subject focuses on answering questions like: How much I am producing? How much could I produce? How do I measure that? Etc. The subject intentionally ignores business models.
So, the question "How do you measure the capacity of a legal team?" (note it says capacity), makes sense. It's the answer I disagree with.
Some legal work product is reasonably fungible, especially at the level of corporate law.
What I think that a lot of management type folks fail to realize, though, is that both the quality of knowledge workers' output and the rate at which they produce it tends to drop precipitously when they are tired. I wouldn't be at all surprised if a lawyer who works 35 hour weeks can get more done in a given calendar period than one who works 90 hour weeks. Big name law firms, though, bill by the hour, and, even if they share this conviction, they know that their clients went to business school, and have therefore been trained not to understand it.
As for my personal opinion, I haven't reflected on it too much, but I think capacity implies a quantitative (edit: measurable may be a better word?) output, but not necessarily fungible.
I'm pretty sure it's due to exactly that sort of hubris that business school folks have invited so much disdain. The domain in which you're operating simply cannot be dismissed as an inconsequential detail.
Tangentially, there is a subset of law firms that do operate as if total hours worked is the only thing that matters. Over the past decade or so, they've been rapidly losing ground to law firms that, by not thinking that way, manage to do a better job of producing the kinds of output that clients actually want.