yeah but dismissing it on a macro scale flies in the face of teams like the 2007-2008 Giants and 2010-2011 Packers, who were middling teams in the first year, got on a hot streak, then won a super bowl and started off their title defense year on a roll too.
But I think that if you look deeper into those teams, you'll also find some other reasons that explain it in a more tangible way.
We hear it all the time with the World Series, Super Bowl, whatever. It always goes to whoever gets hot in the end. But are those teams really winning because they were hot? Or are we saying they were hot just because they've been winning? It's a chicken and the egg argument.
Beyond that, at what point does momentum become something we can see? For example, considering health, roster, etc has been constant all year for a .500 team, and they go on a 3 game win streak. Are they more or less likely to win their 4th game? Or if you look at all of the instances an NBA player made 3 straight shots, did they make their 4th attempt at a better than average clip? If momentum was a real thing we would have ways of measuring it, predicting it and preserving it.
Sports are measured by statistics and we can look hard for trends when they really aren't there. A Player who shoots 50 percent won't literally make every other shot. Just like a coin flip won't actually alternate between heads and tails in each turn.
To me, momentum is something you feel when things are ALREADY going well. It can give you the feeling that you are playing with house money and that can be a good thing. Maybe you take some chances that you wouldn't ordinarily take and they pay off, but maybe they don't. We tend to forget all of the events that don't support the theory because they aren't memorable.