Since the enemies scale to your level, is there ever any reason to increase monster experience on the group as a whole (through artifacts or royalty points)?
From what I have seen your points are better spent in loot hoarding and given artifacts only have 10 slots Its better to max that out with modifiers that help in battle or increase power gain if your running off of abilities and not damage output
To be fair, even if the enemies scale to your level, at level 1 an enemy ten levels higher will swiftly murder you, while at level 100 you barely care. Each level fractionally reduces the actual difference between your enemies and you on deeper floors.
But yeah, it’s not worth royalty points early on. Spend it on Spoils of War / Loot Hoarding / other Prize Stuff, as that’s what increases your asymmetric power (stuff your enemies never get at all, like full Nether teams, legendary enchants, perk points).