Woo there was druids in Darion, perhaps in druid shop? That is an original choice, eventually I have some in my current game but didn't notice because that's a troop I didn't found useful, but I can be wrong.
Yes Royal Thorn are a problem if you don't have sacrifice. I didn't used them often but in some special fights (kraken, giant spider, karador) because either I get them too late and their fire weakness and low initiative is then a pain, either not find them easy to use because of sacrifice.
Myself I'm using in Darion Ancient Bear, Archmage, Inq, Priest in almost all fights. And with that base, Cursed Ghost or Alchemist, and in last part of Darion I added Royal Snake 5th choice. But well in few fights like with Tiberus I regret not have a non magical long range, like to easily kill the evil books.
EDIT: I forget, at beginning I was also using Horsemen, until the pack was too low for my Leadership.