What did Putin gain from this?
He just got the east-west air corridor over Ukraine closed raising the cost of West-East air travel on the heels of the US levelling sanctions on his companies a few days earlier.
It’s called Tit for Tat. This now gives him bargaining power to get the sanctions lifted and more.
He also wants Kiev to recognize his thug Donetsk puppets as a legitimate government and this will be part of the negotiations.
Recognize Donetsk thug government, then there will be peace and missile batteries come back to Russia, and air corridor is reopened.
Why send an army in when you can accomplish your objective by shooting a plane out of the sky and holding their dead bodies as hostages.
Take a look at my links. It is not clear at all that Putin had anything to do with this. People who hate Russia like to think so. Keep in mind any position 0bastard takes is likely to be wrong, and at the very least his positions should be looked at VERY CAREFULLY if one is inclined to agree with him. 0bastard hates Putin because Putin took the side of Assad instead of the AQ/various jihadis in Syria, among other reasons. And entering a war with Russia would be devastating for the US. And since 0bastard is tasked with weakening and wrecking the US, that is his likely motive here.