> Let's, for the sake of argument, say that the west was orchestrating regime change in Ukraine with the end goal of regime change in Russia, knowing it would lead to war.

OK, let's play this game. The logical fallacy here is the relationship between regime change in Ukraine and Russia. These are two distinct countries. It's like saying someone wanted to influence the outcome of the election in the USA to cause regime change in Canada. (I use this example because we know Russians were influencing the elections in the USA.)

A simply more unsettling conclusion from this narrative is that if there is a causal link indeed, and Ukraine taking a pro-EU direction can cause a regime change in Russia, it means that the basis of the latter is very weak - so weak it has to start the war to prevent its fall.