How Different Were The Stalin's Soviets From Tsardom?

For the sake of simplicity let's reference the Tsar in the 1900s and the Soviets in the 1930s, how similar were they institutionally and ideologically?

I admit that I'm just getting into Russian history but there seems to be so many similarities between the two. Sure the Tsar claimed divine power whereas Stalin claimed collective leadership, yet in practice they seem similar in their coercion.

There's the oppression of dissent, often through violence, the propaganda of the good old Tsar/father Stalin, the inequality between the old aristocracy/soviet bureaucrat and the peasantry/forced laborer, the degree of social control both attempted.
Ideology was almost completely different. The legitimizing principle of Imperial Russia was a combination of tradition (the Tsars had ruled for centuries, and their continued rule was considered the natural order of things) and religion (the Russian Orthodox church attributed the same role to the Tsars as the Greek Orthodox church had assigned the the Byzantine Emperors). The Soviets, on the other hand, explicitly rejected both tradition and religion in favor of Marxist social theory; they anchored their legitimacy in the inevitability and desirability (under Marxist theory) of Communist revolution and in the claim that the government was formed from the Workers and Peasants of the Soviet Union and represented the interests of the aforementioned Workers and Peasants.

Institutions also differed significantly. In Imperial Russia, authority flowed downwards from the Tsar: all officials were accountable to him, and when there was an elected legislature, it existed by his sufferance and only wielded the power he assigned to it. The Soviet Union, on other hand, had three parallel sets of governing institutions, all nominally bottom-up and democratic (emphasis on "nominally"). There were the soviets (local workers' councils, which elected representatives to higher-level soviets, all the way up to the Supreme Soviet whose chairman was the de jure Head of State of the Soviet Union), as well as an elected parliament, and then there was the Communist Party itself. In practice, the Party controlled the parliament and the soviets by controlling both the debate and the candidates for office, and Stalin dominated the Party's internal decision-making. Stalin, once he had consolidated his role, had de facto authority that rivaled the de jure powers of the Tsars, but the Tsars' power was an explicit feature of the institutions, while Stalin's came from an extreme form of Tammany Hall style machine politics.

It's notable that for most of Stalin's rule, he was neither the Head of State nor the Head of Government of the Soviet Union. Stalin was the General Secretary of the Communist Party, while the Head of State was Mikhael Kalinin (Chairman of the All-Russian Congress of Soviets, and later of the Supreme Soviet of the Soviet Union), and the Head of Government was Vyacheslav Molotov (Premier). However, both were political allies of Stalin who owed their positions to Stalin's influence and pretty much followed Stalin's lead.

And even though both regimes were hideously oppressive (especially Stalin's which was an order of magnitude worse than the Tsars in this respect), the targets of the oppression were different. The Tsars feared riot and rebellion, and they targeted their oppression on cracking down on unrest when it became overt and trying to find and arrest those who were advocating and organizing for rebellion. The Soviet oppression had three major phases: the revolutionary period, where they fought rump Tsarist power centers (as well as non-Soviet would-be successor states to Imperial Russia) on the battlefield; post-revolutionary purges of non-Bolsheviks who had carried over in mid-level office (especially in the military) during and after the revolution; and finally an attempt to subvert the de jure democratic nature of the Soviet institutions by suppressing any political organization except the Communist Party and punishing anyone who dissented from the Party line. The last was far more wide-reaching and comprehensive than anything the Tsars attempted, and was driven by the cruel logic of subverting a nominally democratic system to always elect the "right" people.