Siberia is perfectly doable with 12-strong+ squad, equipped with mid-late game tech. The solution to the number of enemies (which can reach 68 on the Jack Sparrow, but will be around 40 on John Silver - a third of them very weak, too) is the right amount of firepower to destroy/disable closest enemies instantly, and armor to withstand every weapon that isn't Tank, Baby Nuke or Supersoldier. If you can't do it, you're too weak yet to get endless lasers which are headache-savers.
As for the Organ Grinder, the lure is not monetary, there are Ghoul captures, slaves and most importantly, Life Support Systems to be won (if you need them). If the reward was too much, the player would feel missing out by not doing it. The key to this mission is speed and cold blood. If you finish it in 12-ish turns, you won't take much damage even with completely wrong armor (like Chainmail). Naturally the hospital downtime is high after such a mission, but not if you already managed to get Sickbay and Surgery. If you use Smokeys and well-trained squad, it's merely challenging IMO. It is supposed to be on the high end of the scale as well.