Now, it doesn’t (in general) mean “Is likely to receive, if convicted”, which some people tend to assume, but it also doesn’t mean nothing. And given the fact that upward departure is allowed from the federal sentencing guidelines, but not from the statutory maximums for the offenses charged, it is literally all you can tell with certainty from the charges themselves.
Opinions will differ on this highly subjective question.
> How does this fact aid my understanding of the severity of what he’s done?
It aids your understanding of the potential consequences, not the severity of what he has done.
But humans are made of meat, and words and phrases have connotations. There's a difference in the perception (both to the subject and society) between those two options.
"Cannot exceed" makes it pretty clear that it's a maximum bound, and doesn't imply that the actual number will be any particular distance between zero and the maximum. "Up to" leads the reader to assume that the likely sentence is close to the stated amount.
Honestly, I think most readers will be more familiar with how “up to” doesn’t mean that it is likely to be close than with the meaning of “cannot exceed”, from experience (as “up to” is regularly used in this way commercially), but, yes, unfortunately given only one figure, even if clearly marked as an upper bound, people who aren’t actively critically reading are likely to fixate on it as if it was a prediction of the likely result rather than a bound.
Press releases aren’t designed to scare the subject of the investigation, especially not press releases announcing a plea agreement that has already been reached.
In this case, probably not - 20 years is pretty stiff, and the crime implies that typical sentences are much less than that.
But if the maximum sentence was say... 6 months instead; or just a fine. Yeah - I think that would be useful information.