couldn't happen. the superbowl is too big of a single event, on something that big, the book tries to get even money on both sides. in the impossible hypothetical you propose where no matter what line they offered, they couldn't do that, they'd shut the book down.
sports gambling is bettor vs. book period. The book has a 5% advantage with bets at the spread. The bettor has to win 52.chnge% of his even money
bets to break even. The best pro gamblers in the world run slightly above this with an extremely good year topping 60%.
In regard to lines, Pinnacle sports does the math and sets the lines for almost the entire industry. Pinny sends early lines to the pros, the pros look for soft lines and make their bets. Pinny adjusts from their professional player imput then attempts to forecast a line that will draw even action. In the
end books don't care as much about good or bad lines as much as they do even action. With that said and all their forecasting books routinely
have games with lopsided action, and don't really gaf because one game is pretty meaningless they win some and lose some and go on.