That's totally fair, there's a balance. Maybe a better argument I could make is that I find people often lean too far to the end of being verbose without any real reason to it. You may not want to be blunt or rude either, the balance is in the middle.

For the career fair grad you mentioned, a couple paragraphs would have been my expectation - three paragraphs isn't off base. If I were them I'd want to say I want to work for you, but I'd also want to at least mention why I want to work there and why you'd want me there. To me that extra context is a better email than just saying "hire me" in one or two sentences.