As the events of this year make clear, their intelligence is not as good as they think.

I've been saying that for years. We've spent about a decade in a soulless rerun of the Reagan era Russia panic and the idea that the USSR had vast infiltration networks in the West was completely laughable even then.

whereas the Donbas rebellion was always about transferring the region from Ukraine to Russia (or perhaps you disagree?)

I do indeed. If the aim was to integrate the Donbas into Russia the time to do so was in 2014 when the Ukrainian army was in no position to fight and not ideologically hardened. Mostly the Donbas militias were not getting the logistical support you'd assume they would get if they were supposed to form an integral part of the Russian state. The people of Donbas found themselves in a similar unhappy situation as the KPP in Syria. They had to accept Russia's/the US' help and effectively become proxies since there was nowhere else to turn.
As far as I can tell the Russians wanted exactly what was on the tin: Minsk2. They grabbed the part of Ukraine they really cared about in 2014 and would have been happy enough to keep the rest in a state of neutrality while raking in euros hand over fist. Of course once the Ukrainian electorate voted the supposedly more pro-Russian Zelensky in, yet the renunciations of the peace treaty got if anything more pronounced all to applause from the guarantors in France and Germany they were left with the option of slinking home in humiliation or flip over the table in rage.