For enemies, attack move towards ghouls kills them without needing to click on them. Ghouls are fairly colorful and easy to see when multiples are up, but if he is ar 4 stacks then his ult is running and you probably should be trying to kill him unless you can burst and dash away.
The slow auto reapplication on a slightly larger range might be good, but right now it is such a weak slow it might as well not even be there. If you don't land the slow directly on top of an enemy it is never going to matter you won't be catching up to them anyhow. As for his passive damage reduction, he is already oimited to 15% max at lv 3, and at 6 he maxes 20%, I don't think reducing it in the early game is fair to him as he is already pretty squishy to all ins early as it is, and later in the game his issue is more that of being kited (like all juggernauts and melees without 2 or 3 dashes in their kit). The scaling passive damage boost only affects his basic attack (auto attack) so any boost to that would probably end up being less than a 2% increase in his total damage and probably far less than that to be honest.
I want Yorick to get buffed more than the average player, but I don't think these changes resolve any of his issues at all, both playing against or as him. The health bar system and decay I completely agree with though, it always seems odd to me that his ghouls just kill themselves all day, often missing out on an attack or two that they should have gotten in but didn't just because of some random AoE or an attack move catching 'em.