I don’t really understand the tooltip. I googled it and the best I got is that up to 10 enemies get ticked for 100% weapon damage, where the rune itself says it’s 100% up to 10,000% damage. There is no explanation as to how you reach that. If it’s up to 10 enemies and they are considering it to be accumulative, that’s still only 1,000% damage. So either the wiki is wrong and it’s 100 enemies or there’s some other mechanic to it. It can’t be over time because it only lasts so long.
10 enemies times 100% damage for 10 seconds is 10,000% damage during LotD.