Gurkhas are the best mercs in the game from a cost/benefit perspective. I have no idea how you think they are not good. Only the flame tank is better.
FROM a cost/benefit perspective!!!
As I said, I use it a lot, but only because are the best mercs, what I think, and there is an achievement about hiring mercs.
And ocasionally some quests will appear too.
But otherwise, they are useless. 6 Gurkhas are worst than 2 Riflemen immo, at least I don't find a place in my army for them at all, they die in a second.
If I were not to hunt animals, I won't probably use any mercs at all, sword blessing instead.