The problem is that perhaps the only "advantage" of the dissolution of the Soviet Union is that all of the old theories may be tested.
I understand this to be disdainfully sardonic (from you? never!) but..
1. The people advancing these "old theories" were always pretty dodgy from Mao and Sweezy to all of the bougeoisie prevaricators.
If Machiavellian machinations -- political oppression, ruthlessness, intrigue, and double dealing are decisive, then the motive engine of history is..cruel and aleatory vicissitude? (I choose the term intentionally since it invokes Althusser which seems a fitting "tribute")
1a. If a "new" explotiing class arose -- or even if it was simply the restored bourgeoisie rebranded (a staple of capitalist marketing to be sure) -- then the question is on what basis this class arose, just as you say. There is no valdi way to make the claim without breaking with the tenet that (human) history is driven by class sturggle. For the march of the productive forces we are effectively asked to substitute random chance.
1b. These "old theories" are demonstrably made up on the spot by the bourgeoisie apologists as they come to the realization that history has left them in the dirt. They perceive Darwin has passed them over; far from being found fit to rule Clotho has spun her judgement and they are deemed wanting. So of course they try to change the rules and return to the vagaries of politicking and "cunning" to justify their own wretched continuation.
1c. Soviet interventions (ie Prague Spring) did not really constitute the break that spawned these new "old theories". No one suddenly became weak-kneed over "social imperialism" without some ulterior motive considering that Soviet interventions were present from the outset (Georgia in the '20s..). Some PB radicals lost their nerve..my heart, it is breaking..
2. Lets imagine the worst that petty bureaucratic favoritism ran rampant, and bureaucratic misappropriation was widespread and went virtually unchecked.
So what? Property was still nationalized, the means of production still lay in the public not private sphere, production and allocation still occured in a planned fashion. The bureaucracy did not and could not overthrow any of these fundamentals w/o negating themselves in the process, which seems to be exactly what happened.