First I've read of this line of thinking. The rational makes sense and nothing seems glaringly wrong with this scenario. To your last point I believe it's als

First I've read of this line of thinking. The rational makes sense and nothing seems glaringly wrong with this scenario. To your last point I believe it's also that it secures his corridor to Crimea and will secure the three pipelines that run through Ukraine. Supply of gas is a point of leverage Putin has on Europe. Securing the channels for it and also of the second largest source of reserves (Ukraine's) furthers to solidify that point for him.