Dunno about TFT, but Ghouls make a good substitue tier 3 melee unit for UD in RoC... I think their DPS still outmatches Knights and Aboms when they get Ghoul Frenzy... Not sure though, it feels like it...
2-3 Ghouls on lumber is plenty. Consider the fact that they bring in 20 lumber a load, something Orc cannot match, and Humans can't without researching (and even then, Ghouls move faster, going even faster after they get Ghoul Frenzy). (Can you tell I like Ghouls?
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The UD gold mining is pretty fast, maybe they made the Acos exposed for balance issues, so that UD don't get major resource advantages early (imagine Acos hiding inside the mine a la NE!)
Their heroes don't need to creep alone, you usually get Ghouls or Fiends fast enough to have them creep with the hero.
Some of their weaknesses aren't too glaring. Just need to get used to them, and cover them. Enhance your strengths, downplay your weaknesses, and give 'em hell. :lucifer