Or is it a comparative grey matter evaluation in time and pressure constraints?
you provide an example, but the luck is in guessing what the opponent would check or not check.
a clearer example is trying to play out of your opponent's prep. you dont know what lines theyve prepared, and youre taking a gamble with each move on whether theyve prepped it or not. they cant prep every possible line in the available time, regardless of how long (ding wasnt prepared for most of gukesh's attacks, with months to prepare)
theres also luck in that your opponent may not have slept well the night before because a car alarm went off at 2AM, so their comparative grey matter evaluation in time was lower than usual, or they just played a tiring long game where they lost, right before this game.
One of the biggest examples of this was in his title defense against Caruana. Every game of that match had been drawn, and in the final game Magnus had a very promising position where he could squeeze with basically no risk.
Instead he offered a draw which was immediately accepted. That sent the game to rapid tie breaks where he casually butchered Caruana 3-0.
And no great player is bad at any time control - they're just 'less good'. Except Magnus - since he's #1 at everything he's just more or less dominant.