I think teams can be better suited to slowdown or uptempo, so I don’t really agree that the non-normal tempo itself decreases expected points per possession. But of course that will be the by-product, if the team is not well-suited to the tempo. In my thinking, this is a much bigger factor with uptempo with slowdown. Generally, I think the penalty of playing slowdown pretty much begins and ends with fewer possessions, period. This leaves less margin for error, and makes it more difficult to overcome an opponent’s hot stretch.
With uptempo, if you don’t have speed, ball-handling and stamina advantages, you are likely to commit more turnovers, which turns extra possessions into a negative.
It really comes down to how I want to try to win a particular game, for me. Am I going to try to win by taking care of the ball with high IQ, good passing, and high percentage shots and rebounding? Slowdown might be a consideration. Am I going to try to win by exploiting advantages in speed and ball-handling and stamina, to maximize possessions and reduce variance? Then I’ll think about uptempo. Now, I probably stick with normal about 85% of the time. But my best championship level FB/press teams were pretty much exclusively uptempo, because I had built that team to do that thing.