Very very cool interpretation of the theme, I love it when the player and the enemies both have the same toolkit it makes for a really interesting dynamic. With that being said if you walk past a wave of enemies without defeating them and then continue to just walk forward, no other enemies spawn so you can kinda just walk endlessly in the dark without any adversity.
I think you should make it so that when the player's Y position gets a certain amount away from an enemy they despawn allowing a new wave to take their place.