Bro production line is not something you can shift somewhere and that too underground overnight.
And not everything can be shifted underground.
If you were producing 100missiles per month pre war but due to destruction of key facilities, your Production is limited to only 10-20 per month, this is a big capability gap and a big achievement for enemy.
At Hanyiah assassination, Iran fired almost 180 Ballistic Missiles in one or two nights alone, but due to suppression of bases during war, Iran was able to fire only 10-15 missiles - that is almost 90% suppression of offensive capability - not a fking joke.
Which nation on earth has been able to achieve this against any enemy?
Again, US is judged against 100% domination standards so its military performance is sometimes not appreciated as much as it should be.