The value of how 'good' a map is (in this context) is itself determined by the value of the wall. So, like I've said, you've made the gap wider. Yes, you've made the maps that are 'okay' to wall now 'bad', but maps that are good to wall have just gotten much better relative to bad ones. Until you push the cost of building a wall into "not worth it" territory across the board, all you're doing is improving good maps and punishing bad ones.111111111 no!
With **** map you will not wall at all, you will play with army. But player with good map will wall with 2x price. So it will be more balanced.
The other important factor here is that the cost of a feudal age army is, itself, lowered by an opponent full walling. You're not going to be able to do much with all those scouts if they don't have a way in. So, again, by making it harder for the players with just 'okay' maps to wall, you're widening the gap.