There is some debate as to whether or not Russia was really trying to take Kyiv. If they were, I can understand the reasoning- it's where the head of the Ukrainian government is. Remove said government and in theory, the war might have been over long ago. Now, I can certainly agree that any temporary peace achieved this way may have just resulted in problems down the road, as the U.S. experienced in Afghanistan and Iraq.
In any case, for whatever reason, they withdrew from the outskirts of Kyiv and focused their military campaign on eastern Ukraine.
As for only sticking with LNR and DNR recognitions, I think that would have been worse than useless. If all Russia had done was recognize them and let Ukraine continue its military assault on the the Donbass republics, I believe people would have considered Russia's recognition of a republic to be worth nothing more than a goodwill gesture. By not only recognizing the republics, but coming to defend them in short order, I think it's safe to say that no one will ignore Russia's recognition of another nation that's under assault by its own alleged government again.
I think it's telling that it only took a few months for the U.S. to go to war in Afghanistan after around 3,000 Americans 9/11 and most of the world was ok with that, but after over 3 times as many eastern Ukrainians, many of whom were ethnic Russians died over the course of 8 years in the Ukrainian civil war, the west is up at arms on the whole thing.
I just hope that this conflict doesn't escalate to the point that one or more nukes are used.