About reponse time, you're not gonna have hammers hitting your treasury from a village next to them, you're gonna have few hours to respond at very least and your def troops should be close enough that they can respond to the threat, especially with forwarding. You shouldn't let your enemy develop a village next to your treasury.
It doesnt even have to be that extreme. A 20h attack could become a 4h one (especially around european nighttimes thats a huge difference).
Also with enough gold you could have a decently reinforced city built up from scratch in under an hour right inside enemy territory. Let your kingdom send def, relocate your hammer there, throw a couple gold more at your screen to feed all that and go to town with your troops.
This feature would just be terrible. A little less terrible for ppl who would want to (ab)use it as or similar to as I discribed. But still enough. You could mabye tweak it (by limiting it to only reinforcing older villages or only x amount of units per day or whatnot) but Id rather have it stay this way