I think it cuts both ways and was largely a function of the indivdual despot, not of the political system.
Ivan the Terrible, despite descending into a murderous madness, died a natural death. The same for Peter the Great, whose policies alienated large and influential segments of his subjects. On the other hand, Nikita Kruschev was removed by a quiet coup and lived the last few years of his life under house arrest. Neither system proved capable of removing their most brutal despots, and both proved capable of removing their more restrained leaders.
However, both Peter III and Paul were removed by palace coups, supported by the Russian nobility. And there was that very awkward episode of the succession to the throne of Anna, when the nobility tried and failed to assert its civil rights as a class. I guess my point is that in modern times at least, under the Romanovs (as opposed to the Rurikovichi like Ivan the Terrible), the throne was always answerable to its most powerful interest group, i.e., the nobility. Even Peter the Great, for all his Westernizing measures, didn't impinge on their landowning privileges and their so-called rights over their serfs.
As for the Soviets, by the time Stalin died, his lesser minions were exhausted and demoralized by the Great Man's ongoing party purges, and only too eager to see an end to it all. They just wanted to lie back on their laurels, relax, and enjoy the fruits of their success. So after Stalin's death (which they speeded along considerably by not seeking medical advice for some days after his stroke!), they made quick work of Beria and his secret files (since he had files on all of them, as they all well knew). And years later, when they wanted to get rid of Stalin's successor, Khrushchev, they did so in a "civilized" manner, thus reassuring themselves (and any future leaders) that if they should ever fall from grace, they would not end their days in the Gulag, but rather, as Khrushchev did, in a relatively luxurious apartment in the center of Moscow, surrounded by family and friends.
So: whereas the Romanovs always had to answer to the nobility, if not immediately, then within the next reign or two, the Soviet leadership only ever answered to itself, and then only when those "other," lesser leaders got up the nerve to make a stand (as it happened, they never got up the nerve with Stalin until he was on his deathbed and beyond punishing them for it).
Certainly the tsars considered themselves answerable only to God . . . which was not terribly inconvenient, at least after Peter I subordinated the Church to state control. Lenin and Stalin held themselves as answerable solely to their Marxist ideology which, taking a cue from the tsars, they claimed the sole right to interpret.
I agree that both approaches to power are more than convenient, but Orthodoxy, whatever its flaws, was never as theoretically all-encompassing and intense a lifestyle ideology as Marxism-Leninism. Orthodoxy seeks to regulate human souls; while, how does that famous saying go, Marxism-Leninism seeks to engineer the human soul. Orthodoxy recognizes the imperfection in humankind; whereas Marxism-Leninism seeks to eradicate that imperfection, and build man in its own idealized image, by any means at its disposal.
That said, I don't disagree with the main argument of your first post. Don't fall off your chair in surprise, Tsarfan, but I do now see a linkage between autocracy and the Soviets. A linkage - not an equivalency. But as I said, my views have evolved a lot in the last several months, in no small part thanks to your own contributions to this forum.