Once should view things through the lenses of nuance.
And, most importantly, compare their current state to what they were before.
"Completely obliterated" might sound hyperbolic, and perhaps it is. However, let us compare the Iranian navy then, to what it is now: apart from small fast patrol ships fitted with DShK and logistic ships, everything, or close to it, has been either disabled or destroyed.
Basically the Iranian navy has been downgraded all the way down to the Somali navy.
Gunboats can be a nuisance, yes, but not a threat comparable to a frigate, a corvette, a missile boat and such.
Incidentally, these gunboats are fairly easy to make. Just get something big enough on which to bolt a .50 cal and there you go.