The point is Oda didn't show him being a badass just so that he can job to Luffy/Law/(Cavendish?) instantly. When we first saw Diamante's power it was meh, Pica's was cool, but Trebol's was holy shit he just threw a ship/hit a fly between the eyes. Those plus the fact that he's with Doffy tells me he'll probably be the executive to put up the most fight. Law cuts him? He can stick himself back together. Luffy punches him, he can capture him. All I'm saying is, he's not there just to get in the way.
Uh haki? If he gets cut/punch, he'll take damage. You're really overrating the executives power levels. If he even does stand a chance against Law it'll be….........lead poisoning weakness or Luffy screwing around as he discovers his powers.