> Ukraine never had nuclear weapons. Russia is the sole legal successor of the USSR and these were all Russian nukes on Ukrainian territory.

Structuring the breakup so that the nukes are Russia's is not really different than Ukraine giving up the nukes on its territory.

Where did they draw the line? Obviously not all USSR assets are now Russian assets, as Ukraine still has (or had) its own stockpile of Soviet era weapons, and other things like Soviet era airfields.