seems like it would be more interesting if he was at least a little bit charming with Kate and show his true colors when he's talking to Daniel.
*nod nod nod nod* YES. Exactly. It feels like there should be a duplicity to him which underlines Daniel's entire point that this guy is a charlatan and a jerk. Which would be perfectly illustrated if Hathaway were a real smoothie and genuinely made Kate swoon, meanwhile the arrogant attitude that we've seen him display so far is only occasionally present... and more so as his arc progresses. (Plus, though as noted it's great to watch Jamie have fun with such a smarmy character, it would arguably be even better if he got to show some range by being both smarmy AND dreamy, depending on when it suited Hathaway's motives.)
In a way, this "No, seriously, WHY didn't you write it this way?" conundrum is a perfect nutshell example of my frustration with the logic on this show. But it applies to a billion other elements too (which I won't go into because, well we'll only have one more discussion thread, why bother? ;) )