most of the cards after Shadows are way better than everything made before
I agree on this partially. The problem is not the shadow, because I think shadow form block 1, 2 & 3 equals with blocks 4, 5 & 6.
In my opinion there are just 3 problems:
1. The biggest problem is that the fs of the movieblocks have a focus on culture and the post movieblocks on race. That wouldn't be a problem if not the shadowcultures were the same. This makes the fs from the 3 movieblocks weaker against shadow from post movieblocks. For instance the fs from the 3 mb have cards that effect's only cultures like Moria, Isengard & Sauron. The fs from the other blocks effects on race, which is wider. That makes it difficult for the mb blocks, because they have less cards they can use to defend. So therefore the fs from the 3 mb are weaker, unless they can combine with all 3 the blocks from mb.
2. The sitemechanic: Fs from the 3 filmblock blocks do have a different mechanic then post filmblock. They depend actually also more on that mechanic.
3. the combination of my points 1 & 2. The fs of the 3 mb are more dependable on the old sitemechanic, There also sites which interact with those fs. And this is different then the new sitemechanich which makes things wider.
So I think this idea will not work proper with the rules as they are now. It will mean that you'll need a lot of rule-bending and a lot of errata. The x-list for mb-cards will schrunk a little but the r-list and rules will be bigger. Also the r-list for post mb will grow.
The difference with the austrian format is that you can use all 3 of the the mb's: which makes it for the fs able to use more cards which gives them more defence. The only movieblock which is strong enough on it's own is rotk-block. So what you will get is that people will run block's 3 ,4 , 5 & 6.