You have abstracted things a bit too far.
Unless your interceptor system is unobtainium laser system with unobtainium cooling system, backed-up by unobtainium power source, you are going to run out of interceptor missiles (or even Phalanx bullets) way sooner than 'million missile attempts'.
Quite possibly 100-200 Shaheds + half a dozen proper anti-ship missiles will cause you to turn tail.
equally unobtainium as the 1 M missiles aimed at the ship.
Is it? Russia’s making 60k Shaheds a year, and they are in the middle of an active conflict that has other needs.
60k / year = about 180 per day = 7 per hour.
there are so many options from coil guns, to lasers, to jammers, to non-nuclear EMP's, ... that don't involve the caricature of a million dollar missile intercepting it.
You’re proposing largely experimental or theoretical solutions to a today problem.
And the Ukraine war has demonstrated the issues with jammers.
I agree launching 1 M Shahed drones at a ship would be purely theoretical, and won't solve Iran's today problems...