You seem to be missing the point that it happened on the same day as the presidential inauguration. This isn’t a matter of emotional response or anger. It is a matter of national sovereignty.
If the Americans assassinated a Chinese official in Russia by a missile hours later after meeting Putin during his inauguration. Then the Chinese and the Russian do nothing. Likewise, if the Iranians assassinating an Israeli official on Trump inauguration day. Then the Americans and Israelis do nothing.
What do you think said governments credibility will be like domestically and internationally?
You brought up a lot of strawman to fit your narrative .. this is not about 'missing any points'... this is about reality. And yes in the real world, emotions and anger even at the highest levels is very present and very real.
Also Iran is NOT the US or China or Russia. Inspite of what you think, Iran is not invincible nor does it have anywhere close to the power and military capabilities of the US or even Israel.
As such they need to tailor their response very carefully.
And such a response would usually commensurate with the level of destruction the offending party caused.
You can believe whatever you want however I'll stick with me assertion that had the assassination been carried out with large scale bombardment with a lot of human and material damages the response would be quite different than with a very limited surgical strike with almost no colletetal damage.
The fact that it happened on the inauguration of it's leader does plays a role BUT it's impact is insignificant compared to the level of destruction or damages of the strike itself or in this case luckily the lack thereof.