I don't think there is a fear of being imprecise. If anything, it is a fear of speaking plainly as boring.
This is not specific to "Americans". Learn any language and you will have the same impression, and experience the same gulf between textbook usage and everyday usage.
Of course, American corporate-speak is unique from normal conversations, and people intentionally use vagueness to make sure there's general agreement before saying something concretely that might be contentious or cause problems.
This is more corporate/middle class.
There's also a working class register which is very direct and sweary, and extreme insults are actually meant affectionately.
Even more confusingly, the two can overlap, and the same people will switch between them - sometimes in the same setting - with relative equals.
Americans don't seem to do understatement. "My business died" becomes "My incredible journey." Relationships are cross-bred with hustle, so you can be friends with someone and they'll ask you to invest in their MLM scheme.
Instead of using understatement US corporate speaks uses noise to act out hierarchy, to gaslight and to misdirect.
I was talking to someone today who was asked to produce a report. They sent it on time, and then the team lead called a meeting to ask why it hadn't arrived.
The report was literally sitting in their inbox unread. Everyone could see it, but they all went through the motions of pretending it wasn't there and developing an action plan for future delivery.
It's all very David Graeber. So far as I can tell the US seems to specialise in situations where corporate insanity is happening but the sharp edges have been filed off, so it looks like productive activity higher up the pyramid.
Brits say this all the time because they assume we talk like people in movies and interviews do (or they interpret corporate-speak as how Americans actually talk). We use understatement plenty. In fact, the "interesting idea" understatement? I wouldn't even clock it as British because we use that in the US, too. I would say it is a classic example we use here of how you politely call an idea stupid. "Hm, interesting." We don't usually say "that's a stupid idea." That would be extremely rude.
I encounter this same attitude vis a vis Brits and sarcasm. "Oh, Americans don't get sarcasm." We absolutely do get sarcasm (insert claim Brits are being sarcastic when they say we don't get it). Britain is not special in this regard. It boggles the mind why Brits think we don't understand it. The languages are not so far gone.
I tell ya what, "understatement of the year" was not a phrase coined to describe something a Brit said.
You also find observers outside the Anglosphere describing understatement not as a British thing, but an anglophonic thing, including in American speech. https://www.identitytheory.com/anna-wierzbickas-english-mean...
I would go so far as to say that the hedges famous to American English opinion sharing is an example of understatement. "I feel like XYZ" is an Americanism, and it's understatement to the point of re-catorizing a fact as an opinion in order to soften your speech.
I can't tell you the number of times I've heard a Texan describe extremely hot weather as "a bit warm."
Examples abound.
(We also bust balls with our friends, and it lines up with class the same way you describe, including code switching between two registers.)
That is surreal.
I see what you did there!
I'm willing to bet it's a combination of two factors:
1. you are consuming these things in English, and English natives are less likely to say "English has this word that those other people don't" because they fully understand English so it doesn't seem inscrutable, but some other language is kind of "magical an mysterious" to them. See, e.g., the urban legend that the Chinese word for crisis is "danger" and "opportunity." https://en.wikipedia.org/wiki/Chinese_word_for_crisis There's a whole cottage industry around "that foreign language is so cool compared to English"
2. "this language can say X but another language cannot" is invariably wrong
So 3–8%.
Nothing to do with pretention and everything to do with impossibility :D