Well, while you may be partly correct .... may I remind you with these harrowing pics of death & destruction by Russian missiles on ordinary civilians.
I doubt he world would comedown on Ukraine like a ton of bricks as you assume, as they would know why Zelensky would nuke Moscow after what it has and is suffering from Russia's illegal invasion.
Why wouldn't one nuke Moscow, Ukraine has nothing to lose ....it's being destroyed, and thousands upon thousands murdered. Ukraine didn't start a war with Russia .... RUSSIA INVADED ANOTHER COUNTRY. If I was in Zelensky's position, one wouldn't hesitate to wipe Moscow off the face of the earth. imo