And heck, if the whole thing had taken a few minutes longer then all three of them would’ve been blown up anyway and the galaxy would never again have to worry about space gurus who have a very selective moral sense when it comes to violence, and also turn irreversibly evil when they lose their temper.
I feel like that was kind of the point. The Empire’s done for anyways, might as well stall Vader and Palpatine so they can’t escape, and maybe save your father from eternal damnation too. Luke explicitly says that he’s stalling for time in the scene itself: “Soon I’ll be dead, and you with me.”
And also, Luke didn’t turn irreversibly evil when he lost his temper. That was kind of the point too. Palpatine was cocky enough to think that Luke would instantly want to kill his father and turn evil just because of his brief moment of anger in the duel, but Luke proved him wrong by throwing away his lightsaber and declaring that he’d never turn to the dark side. Compassion is a stronger force than anger.