When considering soft things like conversational flow, try not to get too focused on the use of any one particular word. Look to the intent behind the phrase.

When considering soft things like conversational flow, try not to get too focused on the use of any one particular word. Look to the intent behind the phrase. "Wow, that sounds hard" is fundamentally 1) an expression of genuine acknowledgement, and 2) an opening to learn more about what is clearly important to the person you're talking to. The skill is in finding something about your partner that you can say these things honestly about. You do that, and whatever actual words you use to express it don't really matter that much. The emotional intent behind your words will ring clear.