Your instincts are correct. Here are the data on parlays, from yesterday's Wall Street Journal:
FanDuel, which controls about half of the national online betting market, according to Eilers & Krejcik, leads the industry due in part to its success capitalizing on parlays. Last October in Illinois, for example, seven out of every 10 bets placed at FanDuel was a parlay, according to data published by the state’s gaming board. FanDuel made about $29.60 for every $100 bet on parlays, compared with $4.80 for every $100 in non-parlay bets.
N.B. Sorry to post about "FanDuel" rather than "FanDual". That's their name.