Again, to appreciate the 40 time you need to know how it was timed. The old numbers from years ago were all hand timed, and the hands are slow, so hand timed numbers tend to be a bit low, by perhaps .2 seconds. Thus a modern 4.60 laser time is the same as an old hand time of 4.40, and the guy running a 4.37 laser time would have posted a blazing 4.17 hand timed. There weren't a lot of sub 4.2 times in the old days, and there aren't a lot of sub 4.40 laser time today. A 4.73 or whatever, is like an old 4.53. It's not extreme, but it's fast enough, especially since, as bobcatblitz pointed out, while he is at Ohio he should lower it.
To put things in perspective, I remember a player named "Johnny the Jet" Rodgers, who won the Heisman. Was he called the Jet because he was fast? Hardly. It was because of his acceleration, and sideways movement. It was said he ran a 4.8 40, but they jokingly said he could also run a 4.8 backwards and sideways, too.
Brunis has enough speed because he has the explosive acceleration to go with it, and the vertical leaping ability, too.
“We have two ears and one mouth so that we can listen twice as much as we speak.” ― Epictetus