I mean, to some extent, defense will always be stronger than offense—offense always needs to travel to get there, for instance, while defense happens where you are—but the degree makes a big difference.
If, all else being equal, it takes a force of 1500 attackers to overwhelm 1000 defenders, defense is still stronger than offense, but you can still expect to be able to make progress relatively easily.
If, on the other hand, it takes 5000 attackers to overwhelm 1000 defenders, suddenly you have to make very different kinds of calculations about what is worth the cost, and what is even strategically feasible to take without destroying your army's ability to fight.
If, all else being equal, it takes a force of 1500 attackers to overwhelm 1000 defenders, defense is still stronger than offense, but you can still expect to be able to make progress relatively easily.
If, on the other hand, it takes 5000 attackers to overwhelm 1000 defenders, suddenly you have to make very different kinds of calculations about what is worth the cost, and what is even strategically feasible to take without destroying your army's ability to fight.