The reason why I don't like a waterfall sleeve on a business suit is the same why I don't like a drape cut on it: It gives the appearance of (what's the term again, ah yes) "relaxed fit"!
And that clearly belongs into the realms of leisure wear.
Imagine yourself in a board meeting. The numbers of your department aren't that great.
Do you want to sit there in one of those soft sloppy wide cut shoulder and chest coats with a waterfall sleeve whispering:"Whatever, dude!"
You want to sit there in one of those clean as a whistle coats with straight shoulders, proper sleeve and firm chest that's shouting:"Bring it on, motherf*ckers! You got nothing on me! Because I am the best"!