Yes, it was a cultural sphere more than anything else. Just like how Germany and Italy were, and outside Europe, China, Persia, and India, were cultural spheres, often fragmented into many states.
Ukraine and Belarus have managed to evolve their own cultural identities. This is by no means inevitable.
Moscow indeed is a wank (after all, what favours it over any of the other Golden Ring cities?), but everything I've read suggests it was a simply matter of bribery and religion (Ivan Kalita's relation with the church) and luck that ever made Moscow able to dominate the surrounding area.
But is any Russian state which gains the advantage Moscow had after Ivan Kalita guaranteed to unify Russia? If you split whoever maintains the leadership of the Russian church with whoever is the Grand Duke of Vladimir, don't you have a natural state of disunion? Especially if a state like Novgorod in the north is able to remain aloof from the situation. And even then, what is going to encourage these minor princes to sell their titles to the Grand Duke of Vladimir or the prince who holds the seat of the church? And could foreign powers exploit this--Lithuania is the most obvious in the 14th/15th century, but surely Sweden could too, even medieval Sweden might find reason to prolong it based on their interests in Finland/Karelia. The Golden Horde and other Mongol states will fade away, but what about the Tatar successor states of the Mongols? They'll want to have some say in what goes on in Russia, if only out of self-preservation. Really, butterflies aside, can it all last until the age of nationalism puts Russia together? Because what I see from this thread and my own knowledge is that the conditions in Russia were far more conducive to unity than in, say, Italy at the same time.