Is he though? Failing ? It's true he's not brilliant and doesn't understand the intricacies of finance like Harper does, but he is a salesman, not an analyst, not a trader and he isn't in the investment banking division like Gus was.
Maybe I don't understand the high finance environment, but I thought, at least on the CPS and FX desks as portrayed on the show, that the salesmen are pitching ideas that aren't their own, for the most part. Of course they need to have a working knowledge of what they're doing but I thought the research people were the brains(like Gus' fwb in S1). Salesmen are supposed to bring in new business and maintain and monetize existing relationships.
Back to Rob, he doesn't seem that bad at his job. "Adler liked him". He was doing well on Clement's account in S1, it wasn't his fault Kasper retired and the other guy pulled the plug. And with Nicole, even before the handjob, he did a good job of reviving the relationship. Would the sale have happened if she turned Nicole down, the way Harper did? Maybe, maybe not. But considering Nicole's relationship with Pieropoint was completely soured by Harper(Nicole answered Rob's first call with with "what could someone from that institution possibly want?), Rob did a good job of bringing her around.
On the show they make it seem like whales like Kasper, Felim, Jesee Bloom, Nicole etc. can do business with whoever they want, and it's probably the same in real life. So in sales what makes Harper intelligence more virtuous that Rob's charm and ability to get people to like him? Why is one considered merit and the other cheating? The way I see it, what matters is whatever gets and keeps the business.