This changed damage multiplier is only for defenders, not buildings.I don't think you can destroy any of the defensive tower of a D base with 8 barrage
In fact,most players equipped with rapid deployment radio to Tank Depot and bunkers , even barrage with 20x damage cannot destroy a protected defensive tank at once.🙂
Barrage only function is to take out a few of defensive infantry.I've never seen it used after the industrial age.I suggest give it 20-30× damage against defenders, which will allow it to destroy tanks(×1) or HT(×2).