The real question it is, Why IRIAF bought the Su35 when something out of there (J10CE) have performed so brilliantly?.
The Su-35 and J-10CE are two completely different fighter jets. Heavy fighters and medium fighters cannot be compared; their roles and uses are entirely different.
From a practical technological standpoint, the Su-35's advantage lies in its inherent combat capabilities, while the J-10CE is a node in a system-of-systems air combat system. When both are part of a complete system, a single J-10CE fighter can easily defeat multiple Su-35 fighters and escape unscathed, leaving the Su-35s with no retaliatory capability (you can observe PLAAF air combat exercises for details). When neither engages in combat without system-of-systems support, the J-10CE has a slight advantage (more advanced radar and air-to-air missiles), but the outcome depends on the pilot's skill. In routine multi-mission operations, the Su-35 completely outclasses the J-10CE (the advantage of a heavy fighter).
The problem is that a complete air combat support system is extremely large and expensive. The PAF has a long history of cooperation with China, including with its long-range early warning radar, ground-based air defense systems, command systems, and data links. Therefore, after procuring the J-10CE, they quickly achieved operational capability. But Iran needs to rebuild everything. This will be a very large expense.
And the answer is there. For example, if China sells J10 (or other advanced jets) to IRIAF then Saudi arabia would never knock again the door of China as intermediary for diplomatic solutions, for example.
And let´s be honest. China have been sensitive in the deal of US tariffs rebate for some rare minerals, let alone to have complaints from at least 4 countries in the Middle East (Israel, Qatar, Saudi Arabia and Jordania), not to mention even Egypt or Turkey.
If China wants to keep his status quo in the region, must avoid change equation, and that sell would do it.
And Russia does because Putin himself falled in the same category than Iran or North Korea. So that makes all in all "brothers of misery".
Regarding the understanding of international politics, given our different social environments, we cannot reach a consensus.
I have already stated my point of view. No one can pressure China for selling weapons to other countries, but they can pressure the purchasing countries.
If Saudi Arabia or Qatar are concerned about China selling fighter jets to Iran, they can purchase more advanced 5th-Gen fighter jets from China, or simultaneously purchase J-10CE+PL-15E fighters from China for research or countermeasures. China's weapons systems are open to Iran, but also to Saudi Arabia and Qatar.