Shared fate, shared currency (US Dollar), shared Karma, I agree. Though one can break out of all three somewhat
Absolutely. Our national karma does not obviate individual karma. Nor does it obviate the karma of good things done for Israel on the national level.
But something this negative overwhelms a lot of it. Having an argument with a friend doesn't change things much. Spitting in his face, slamming the door on him when he is being pursued by enemies and setting yourself against him can wipe away every good thing you have done for him in an instant. The cause and effect in that shouldn't require any deep esoteric meditation to understand.
The effect of national karma on the individual, when it is really bad, is like being in a great earthquake. Some are near the epicenter and some aren't. Of those who are some are squashed immediately. Especially those who didn't build for it. Those who built well and stocked food, water and medicine may do better. But every survivor has to deal with the aftermath in some way.