Forgot to mention Timber Hill. Those guys had the most stress-free job on the planet. They gave up huge edge sometimes, but I'm sure the guys upstairs were locking in much bigger winners. Cushy job, mediocre salary, but maybe they all got IBKR stock and were multi-millionaires. Would explain why they were always in a good mood and joking around. They weren't really traders though, basically just human robots quoting from a handheld tablet.
There were certainly some very sharp cookies working for Timber Hill on the trading floor but the real mathematicians and brainpower were pushing the buttons and writing the code on the trading desk. They were ages ahead of the others in the game.