It's always bad to be without ranged units, so I already mentioned above that I make them without invisibility.

Replace Stalkers with Assassins? What's the point? I only did that in the game when playing as Eyrin because she has a cart and you can organize a prolonged battle and take out high-level, low-initiative neutral creatures. There's not much point otherwise; why do you need ranged units when you have Stalkers and Fury, which, with the right tactics, can act as ranged units and transform? You can even play the entire game with just them. When playing as the Elves, I never felt the need for ranged units. And as already mentioned, Fire Mages solve everything.