It seems that interrogating oneself over Defend is in the air, so here is my shot at it.
My foremost trouble with this move is its temporality.
First, when it triggers, on a success, nothing really happens in the fiction. But on a 6-, the GM gets to make a move. It’s weird. Second, what happens when the holds are spent? Not very much.
Secondly, with the hold mechanics, I feel like a pc shouldn’t be able to defend again. Because if the they could, why didn’t they get more holds the first time? What does it means that the holds are spent? As far as I know, other hold-spending moves are usually for more abstract/unique things, giving something like a number of charge for a per-session effect or things like that. They depend less on a fictional trigger.
Now, players and GM may work together to move the game from there to a place where defend is less desirable, but it always feels artificial to me.
I feel that defend should work very well with no holds, as an “instant” move, like Hack n slash or Volley. Like this (untested): When you rise in defense of a person, item, or location under attack, roll+Con. ✴On a 10+, choose 3 from the list below. ✴On a 7–9, choose 1…