From a technical and theoretical point of view, Iran may not be an unassailable fortress for the US military. But, at acceptable political if not economic cost for the aggressor, it pretty much is.
Of course, never rest on your laurels as you said, do always consider worst case scenarii and do plan accordingly. Also, this is a permanently ongoing process bound to last until the day on which the enemy is defeated.
Concerning America's black projects, the issue is that the mere fact of their probable existence does not allow us to invalidate what we can establish from publicly known information, else we couldn't operate any simulations nor could we really discuss the topic at hand, since by definition nothing is known about these secret projects. Also, Iran too has covert arms programs.
But, to the best of my knowledge the outcome of a war has seldom been determined by one or even several secret weapons alone - the Asian-Pacific facet of WW2 representing perhaps a notable exception, with the US regime's use of nuclear arms against Japanese civilians. However the latter is clearly a weapon of unusual destructive scale and thus of unequalled relevance to warfare. Such overly game-changing single devices aren't invented every day to say the least.
In the grand scheme of things therefore, I wouldn't lose too much sleep over US black projects while acknowledging the possibility.
What I was referring to, is his analysis in the following weblog article from November 2020 (you were referencing the same one, I think):
https://patarames.blogspot.com/2020/11/irans-path-to-second-strike-capability.html
It is a complex enough issue. Iran employs both the cavern shaft basing method and the railway-wagon / open-air pit method. The latter allows for a higher rate of fire at comparable degree of survivability. The author concludes his piece in the following terms:
"The concept brings Iran closer to achieve a capability no other country has: Deter nuclear powers from a preemptive counter-force strike by conventional means."
That being said, even if Iran's hardened bases might be defeated by multiple nuclear (bunker buster) strikes, Iran also uses the buried missile container method as well as mobile TEL's which blend perfectly into its topography.
I would therefore say that given sufficient numbers of missiles affected to each of these launching methods, it will be extremely hard if not practically impossible for the enemy to achieve an efficient and timely enough suppression of all theses assets in a manner that would preempt the severe BM retaliation which has so far successfully deterred military aggression against Iran.
I'm not doubting this at all. Indeed, it's certainly not public opinion that will make them think twice.
But, given such a precedent set by the US, subsequent adjustments of Russian and Chinese nuclear first strike doctrines, especially with tactical nuclear weapons surely will.
Well, let's try to do the math: years ago Iran had - at the very least - 31 underground missiles cities, in reference to the Iranian military commander's statement according to which they've constructed a minimum of one such base per province. I would suggest 50 underground missile bases, perhaps even 60, 70 or 80 might not be an exaggeration.
Now as you explained, the enemy would have to achieve several nuclear hits per base. It doesn't seem very feasible with 100 or 200 missiles.
And this is without mentioning thousands of TEL's and buried missile canisters - as well as an even greater number of decoys fielded by Iran.
Even the theoretical destruction of Iran's known nuclear sites by means of atomic weapons, will not be sufficient to stop Iran. In the immediate aftermath of this sort of an event, Iran will leave the NPT and initiate a massive nuclear program at perfectly unknown locations and at full speed, in addition to having each and every potential spy, informant or fifth-columnist executed.
In the end, nothing short of a fully fledged invasion can prevent Iran from developing nuclear weapons, should Iran actually decide to do so. And we know that the cost of such an endeavor will not be bearable to the enemy.
Here the conclusions stemming from the sequence of events aren't taken into account: the point is that the zionist regime cannot afford nor tolerate the social and political costs of 1000 ballistic missiles getting unloaded onto Tel Aviv. Neither can the US regime, by the way, largely controlled as it is by zionist and related oligarchic networks.
In other terms, whether or not the zionists would then proceed to launching their nuclear-tipped ballistic missiles is no longer relevant, since it won't even come to this eventuality, considering that they cannot stomach the 1000 BM's they know would be coming their way in response to an actual military aggression of Iran.
Hence, Iran has already established credible and solid deterrence with purely conventional means against all out military attack by its nuclear-armed foes. Quod erat demonstrandum.