There is considerable variation in the heights of the minis. The Werewolf Lord (large) is actually fractionally higher than the Nalfeshnee Tyrant (huge) because his arm stretches up quite high, while the nalfeshnee is rather short and squat.I just did a quick measurement of the ones you mentioned and these were their approximate heights:
Werewolf Lord -> 89mm
Feral Troll -> 65mm
Mountain Troll -> 89mm
Fomorian -> 111mm
Nalfeshnee Tyrant -> 87mm
Orcus - Prince of Undeath -> 161mm
Gargantuan Black Dragon -> 197mm
Gargantuan Blue Dragon -> 147mm
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