But the West also underestimates, for example, cheap Iranian drones that can be easily mass produced and cost much less than the missiles to shoot them down.
No, it doesn't. It failed to anticipate the large-scale transfer of Iranian loitering munitions to Russia for use in that role, it didn't underestimate their utility. And once they started showing up, the West started supplying more cost effective countermeasures, like the Gepard, which use autocannons rather than missiles.