I thought in 5e you could get XP for defeating foes, not just killing them.You get experience in D&D by killing things. It's in the rules, so I learned it..............in the rules. Without killing and being intimately familiar with killing and people trying to kill them. And before you go on about how NPCs in 5e don't need stats and levels, a champion who has to fight does. They need everything a PC needs for combat, since a PC may end up fighting him.
And I didn't know there was any rule in 5e that NPCs need to earn XP to gain levels; or to put it another way, I dind't know that in 5e the XP rules were a model of how things work in-fiction as opposed to a device for establishing the progression of the PCs.