Its not that either. Vegas can't "balance the books" every game. They have a rooting interest in almost every game.
Your version is correct but the other version dominates conventional wisdom. That is never going to change. People love the image of mysterious men behind the curtain who have inside information and somehow know where the money will go and what the result will be. They tweak everything to balanced action and love it when the public hands them victory via juice no matter which side prevails.
Meanwhile I used to watch sportsbook manager Nick Bogdanovich kick the tall file cabinet at the Horseshoe night after night while desperately rooting in the sides the house needed. He intentionally wore hard toed shoes so he wouldn't hurt his toes. When famed poker player Doyle Brunson wagered $55,000 on every bowl game in 1989 it severely slanted our outlook on all of those games. During the Miami/Alabama matchup in the Sugar Bowl, Nick was sweating the final minutes to such emotional extent he was basically crying. During Alabama's final drive Nick put his hand on my shoulder and said, "I swear, Gary, if we can somehow pull this one out I'll never complain about another result as long as we're here." The 3 or 4 of us in the small office all broke out into laughter. Nick was guaranteed to be whining about something the next day. Very good guy who is still in the business at high level, but gad did he sweat any result the house needed. Even on slow nights he'd be calling me from his home and asking me to check the computer and read out to him what side we needed in every basketball and hockey game, and for how much.
That is reality. It is hardly balanced action. I have no idea how anyone can think that you get a steady stream of equal tickets on both sides and equal money on both sides, even if the line never moves. The joint across the street can be heavy one way while you are heavy the other way. But it doesn't make sense to move the number because every other joint is at your number. You are going to "buy a bet" on a number that nobody else is using.
As I mentioned last week, a pointspread is indeed a prediction of the outcome. It is a prediction of the final score. I got chief Nevada oddsmaker Michael Roxborough to agree to that on the Stardust Line radio show nearly 30 years ago. Roxy was one of the few guys in that town who knew what a joke it was that outsiders held Las Vegas in such awe. He didn't mind admitting things that some of the sportsbook managers would never say in public. Those managers are the worst of the worst in wanting to pretend they have special formulas to produce the sacred pointspread. What a farce. Take away the publicly available power ratings and they have nothing. They would be scrambling to know which side would be favored, let alone by how much.
BTW, there was money on Jacksonville today. The spread dropped to Dolphins -3.5
But to demonstrate the absurdity of pretending that the spread is not a prediction of the outcome, the Dolphins one-team over/under betting line is 21 points. The Jaguars one-team over/under is 17.5 points.
Gad, where did they get that? Did they guess? Did those sound like logical numbers?
Or did they look at the relationship between the spread and over/under? Let's see, that would be Dolphins favored by 3.5 points and a total of 38.5
Nope, no way to get to 21 and 17.5 from there. The pointspread and game total are obviously not a prediction of actual points scored or points allowed.