Sandblast

The condition does all the work here: five damage kills nearly anything white would want dead, but the spell only fires while the target is committed to combat. That restriction is the trade white removal of this kind has always made, going back to designs like Chastise: white does not get to point at creatures the way black and red do, so it gets to punish them for entering the red zone instead. The window matters more than the number. An attacker is tapped or about to be, a blocker has already been declared, and in either case the controller has revealed intent before you spend the card. The five-damage ceiling is generous precisely because the timing is so narrow: the spell cannot answer a permanent that sits back doing nothing, cannot break up a combo creature that never enters combat, and cannot kill anything at will on your own terms. It is a tempo answer dressed as removal, rewarding the patient white deck that lets an opponent overcommit to a swing and then blows out a single attacker for clean profit. The target line reaches blockers too, which turns it into a race tool from the other side: when you attack and a creature is thrown in the way, you can burn the blocker out of the combat entirely, keeping your attacker alive to swing again next turn rather than trading it away. What sits it below the burn-anything spells of other colors is exactly that narrowness: it names its price up front, where unconditional removal never has to.