I don't know why Iran didn't get modern Chinese weapons the last 10 years. Modern weapons,not trash. Was it the Iranian leadership's fault? Was it the Chinese who wouldn't sell fighter jets,bombers and AA systems to Iran? For 15 years Iran has been trying to get Su-35s from Russia,not managing that. Trying to get S-400s,trying to get S-300s,trying to get what? Nothing.
Iran's big mistake was to spend billions and billions of dollars on ballistic missiles,cruise missiles and drones. Iran gambled all their money on unconvential warfare and this is the result. And most importantly,spending all that money while doing nothing to tighten counter-intelligence. Dozens of billions of dollars spent on proxies in Lebanon,Syria,Iraq,
Yemen,Afghanistan,Pakistan,Palestine and elsewhere. It worked for a while. It proved a failure in the end. And when I say Iran,I mean the mullah government,the leadership of the clerics and their IRGC.