If I share a project with an American friend and he says it's awesome, I still don't know whether he liked it or not.

If I share it with a Polish or German friend and he says it's "not bad" then I know he is really impressed.

It's not "fake" - it's cultural differences where what is intended to come across as polite by Americans[1] can be seen as insincere by people from elsewhere. On the flip side, Americans often view foreign behavior that's intended to be neutral as unfriendly, uncaring or cold.

1. e.g. lots of smiling, use of superlatives like "great"/"amazing" to describe mediocre items/effort/results

Oh yes.

Execs are ‘super excited’ about everything. There is no dynamic range at all. They appear to have no opinions and no judgement because their opinion is always that everything is awesome. When the audience knows that stuff is either normal-level ok or actually fucked up, this message is insulting to receive.

Worse, it trains people downstream that shiny happy is the only valid comms. Hard to escalate a concern when you don’t know how to start the message with how super excited you are about it.

It drove me crazy during my corporate period.

Yeah, absolutely.

At least to my British ears, Americans rarely sound authentic.

Its always grandiose statements and elaborate smiles.

Speaking as a Brit, our national trait is generally too understate things. So even saying what you mean, directly, comes off as a bit immodest and hyping it up in sales pitches sounds shady.

Americans generally say what they mean a bit more, so I think their mid point is just different.

As other comment suggested, the way I see it Americans are addicted to hyperbolas. Instead of "Thank you" it's "Thank you so much". So when you genuinely want to thank someone because that person went above and beyond (saved your life, avoided you a substantial hassle, etc.) then it's difficult to convey that.

As a Brazilian, I also find that annoying and unnatural.

Beyond just American, they are trying to emulate Jobs style without his genius for presenting in a compelling and attention grabbing way.

For example when I buy coffee in America the barista says “awesome!”

I think they mean well. But it feels weird.