@Valsined As the players level up, the exp that they got will decrease even if theykilled the same monster. Besides that, usually they will be in a party and the exp divided according to the game (equally divided/ most attack/ party lvl balance/ etc).
Here we see that Ian (MC) grinding his level with him and the wolf Ly. Ofc his exp will also be divided up like the post forum said. But compare him to other players where they party up then it will makes sense that Ian level up faster than other summoners who is most likely in a party of 5/6.
if my memory is correct he kills higher lvl monster but it's been a long time since I've read the novel.
Edit: Also thank you for translating this, I'm loving it