Look at how many s-300 batteries Ukraine had. They successfully kept the Russian air-force at bay for more than one year so far. They are running out now, but to date their long-range AD systems have done a remarkable job. If they had domestic production capabilities they could probably sustain it for much longer rather than having to rely on the West for AD hand-me-downs.
While the US (and Israel) have far more capable air-forces, the lesson is clear: Iran needs to mass produce 3rd Khordad, 15 Khordad and Bavar 373 batteries ASAP. Dozens of batteries of each at a minimum, especially the Bavar 373.
4 batteries of s-300PMU2 is an extremely small number. (Plus 1 potential battery of the older s-300pmu1 allegedly acquired from Belarus.) It is disappointing that the Bavar-373 is still not in operation with even one battery, 4 years after it was unveiled and declared operational...
Iran is 3x the size of Ukraine. 20+ batteries of Bavar-373 is the minimum. I presume Iran can produce that with not more than 2x the amount they spent on the 4 s-300pmu2 batteries ($800 million x2 = $1.6 billion).
Turkey paid $2.5 billion for 4 batteries of the s-400. Investing in mass production of Bavar-373, with Sayyad-4B and upgraded radars, is a much better allocation of capital than the export version of the s-400.