Sad that my first post in ages has to be a rant. First of all I'm super disappointed with the Resistance due to ridiculous resistance damage pointed out by OP, secondly with the discussion here.
Maybe let's start with discussion - OP has pointed out a huge flaw, and argumented this both historically and gameplay-wise, and people are tutoring him how he should play to handle this dumb mechanic. It's like... OP is pointing out how stupid is new Necromancy mechanic, which is super dumb historically, and causes ridiculous damage gameplay-wise, and people are saying to him: "Jeah... if you weren't a noob you would place radar stations near frontlines, everyone knows that radar prevents usage of this new magic."
That's not the point! Adding Necromancy is a problem, that's a WW2 game, and this is straight ridiculous! We know how to handle this, but we do not want to be forced to do so, we want a good game about WW2. And I'm using this necromancy example because that is how I feel about level of fantasy this mechanic invokes. As already pointed out causing this amount of damage by resistance movements is pure fantasy. It looks like Warsaw Uprising is happening every five days in each country... just a casual day in occupied country. I guess the game cover-art should not be a badass gestapo guy approaching covered French, but terrified poor German soldiers, taking cover in a bulding, surrounded by horde of well equipped and blood-thirsty partisans - the most dangerous army on planet.
So, back to the main topic. I can't believe someone though this is a good idea. Someone has designed it, someone has given approval, coded and then tested this... lot of gates had been passed, and he receive it in this form. All this by Paradox who I love and respect so much. How this had happened? Don't get me wrong, I love the idea of resistance and uprisings, heck, that's probably a feature I wanted the most! But not done this way...
I fear someone simply went with the logic - "hey we're making all this effort introducing this mechanic, that we really need to make it count." That is not the right way...
I guess everyone understands that game is not a super realistic WW2 simulation, but on the other hand lot of people love the game as one of the ultimate WW2 experiences in gaming and some level of realism should be maintained. And unfortunately current resistance casualty rate is as far from reality like necromancy and orbital bombardment and it has to go. If you agree with statement "Hey this is WW2 game, you should remove this necromancy feature." Then frankly you should agree that casualties caused by resistance need to be nerfed in a MAJOR way.
What scares me the most, even if Paradox is to nerf this casualty rate (in hopefully near future), I fear they will lower it by 20% tops... while truth to be told, 80% nerf is minimum which should be done, probably 90% would be perfect.