I think they're taking 100% damage from AOE... 3 ticks+stride would kill if I'm right. There shouldn't be enough AOE in this clip even with 4 ult ticks to clear the ghoul.
I added the spoiler tag because I'm actively formatting a spreadsheet to describe my findings.
Do not misinterpret my post to claim Lethality is as good as it was - it is not; however, when you compare level 20 Yorick to level 18 old Yorick against an average level 18 ADC who has ~110 armor a 4 stacked E deals 24.5 (49 total) less damage.
I believe it is fair to compare the new level 20 to the old level 18 as the top lane quest also grants significant bonus XP, so realistically you're hitting those level-spikes around the same time. Further, levels 5-9 ghouls deal more base damage without considering the armor shred of E. In other words: significantly better early game, slightly weaker mid-game, much weaker mid to late game, slightly weaker true late game.
I believe the real reason Lethality is significantly weaker is the ghoul's effective HP vs AOE is tremendously lower. Also, once Yorick builds % pen in the form of Grudge or Cleaver, then the damage gap would increase. However, if you can manage to land a 4 stack on an ADC without them clearing the ghouls with a single Caitlyn Q, then the damage is mathematically comparable. Obviously, when the ghouls are getting cleared by a single Caitlyn Q, then the damage is no longer comparable.
I think Riot accepted that Lethality builds on Yorick would be trash in 2025 because they knew the top lane quest was coming in 2026, so they basically balanced him around this season and let the build die last season.
I think especially with profane hydra only costing 2850G this season, lethality is not AS bad as once believed. Given the literal increased ghoul damage and Yorick priority levels 1-9, snowballing should be easier. Play aggressively early to snowball if you want to go lethality. Don't sit back and try to AFK scale.
