Yes, Clemson and Oregon and others can and do go super up-tempo a few series each game, and run a handful of plays at warp speed, and try not to change the play before the snap. And - to me - they're most fun to watch when they're doing that (and the offensive players, and o-linemen in particular, seem to enjoy that the most).
But, on most series, and in most spreads, they are (rapidly) signaling in the plays from the sideline; doing a quick dummy count; turning to the sideline for a possible check, based on the defense's reaction to the dummy count; and then proceeding with or changing the play, based on signals from the sideline.
We - of course: rarely if ever go up-tempo; almost exclusively try to ensure we're in the "best" play, given the defensive alignment; and put at least some of the onus for making that determination and change on the QB. We also do all of that slowly, predictably, and then frantically and ineffectively.
We agree on the overarching point: Kelly's spread system is the suckiest of the spreads.
It is somehow both too complex (for the QB), and too predictable; too slow and too chaotic; too soft and too risky.
It wastes and breaks players and - with the exception of 2015 - has never been anything approaching a Top 25 offense, in any meaningful category.