Current questions and answers regarding the map editor.

But 16 assassins is a ridiculous number. Pre-built heroes have many more.

The developers give pre-built heroes whatever they want. In principle, one level 1 creature of the Warlock faction is equivalent to 4-5 creatures of the same level from other factions...
5×16=80, and I think you can have 90 goblins. So, it seems everything is correct.