Even from a pure geostrategic point of view massive proliferation has the most negative impact for larger nations rather than smaller ones.
Whilst nukes don’t really help in a war of conquest (they basically destroy the very land and resources that the war was meant to conquer), they’re far more effective for a nation defending itself - which if getting to close to defeat is highly likey to nuke the attacking nation - in effect nullifying the greatest advantage of the larger nations which is that they have the manpower and wealth to field much larger and more advanced conventional armies.
So even the likes of China would turn against Russia if they used nukes, because China itself does want to expand its territory or at least to control more natural resources (just look at what’s going on in the South China Sea) and if nukes were used offensivelly in a war of aggression it would lead to all the little nations around China to get their own nukes (along with everybody else) by which point China wouldn’t be able to bully them anymore.
And this is of course whithout even considering just how much more likely massive proliferation makes that we destroy part or all of our planet due to some otherwise shitty shit escalation or some nutcase getting control of a country’s nuclear arsenal, something which is bad for everybody, not just the larger nations.
Somebody using nukes in a war of aggression would see every single nation on the planet turn against them, especially the larger ones.