What buffs? Ghouls are still walking exp tomes even on blight, with vampiric aura and unholy aura.
When blizzard tried the last necromancer rework, they revealed that they imagine Ghouls are supposed to be used together with Necromancers, or more specifically Unholy frenzy. That was obviously a foolish assumption. Ghouls with their 340 HP are not even worth to cast frost armor, frenzy or anti-magic shield on. Coil level 2 is already missing a ton of value if you decide to use it on Ghouls because you will never get the full 400 heal. And of course Ghouls don’t live long enough to benefit from vampiric aura either.
In the end the Necromancer rework was scrapped. The sacrificial dagger was changed from a “sacrifice a unit and get heal-scroll effect with burst heal on your entire army” to a tiny regeneration over time effect. And Ghouls are still suffering from insane powercreep to all the other units and heroes.