Because there are specialists for weak units. Trogols are bad on their own, that's why Shaktis are needed. The same goes for Dragons.
Ignat can't handle the situation; I don't know who relies on his special ability or even takes him as a starting hero.
Gretchin – I don't know, but I think I've heard good things about him.
And a specialist for Pikemen or Kentas – that's a huge imbalance (especially for Golems and Fae).
By the way, the same can be said about Galtran. His existence is unjustified from a balance perspective, except maybe on M-maps.