About Kharkiv
You are not looking at a complete conquering of the entire Ukraine. Not with 200,000 troop that was original planned, not with the situation now. The strategic goal is to cut Ukraine in half and take the eastern half without pretty much a fight. Which the axis of advance would be along the Centerline between Kyiv and Dnipro and the southern arm if Russia want to cut Ukraine from accessing the sea of Azov and Black sea.
Not every road junction are important to your military campaign. Kharkiv is far from the Military objective and close to the border, effectively you can start with Kyiv and then push toward Kharkiv would be a better way to go than to push from Kharkiv then move West, because you are pushing Ukrainian into your line, not going over the Ukrainian line to take control of the Ukrainian city, that just not making any strategic sense. It would be a easier war to cut off the western part from the get go and then attack Eastward, as Russia itself is the entire blocking position. All of the Eastern Ukraine border Russia. So to push West instead of go center then push east, you are making your invasion harder for no particular reason. Essentially
If Russia wanted the entire Ukraine, that's another story, but then they would not have start with war with 200,000 troop, considering the population of Kyiv itself is 4 millions, 200,000 wouldn't cut even to occupy the entire Kyiv Oblast.
Also, Historical value is for both of them are ethnic Russian, as they were both "Historically Russian" so you get some sort of "Morale" victory to your people by saying "I save/liberate a bunch of ethnic Russian from Ukrainian abuse or what not" That does not do anything with the strategic goal, and it is not even a morale victory now many people in Kharkiv are actually fighting the Russian.
Why do I believe Kyiv is important to Demilitarize? First, ask yourself how a country is demilitarize? There are only 1 of 2 ways.
1.) Ukrainian Government capitulate - Government dissolved, thus dissolving the entire military, just like what we do in Iraq when we take Baghdad
2.) You eliminate enough of Ukrainian to make their force essentially decimated. A unit with over 20% casualty are combat ineffective, a unit with 50% casualty is not combat ready, a unit with 80% casualty are decimated. So by demilitarize Ukraine, you would need to eliminate up to 80% of the entire Ukrainian Armed Force
Now you tell me why is Kyiv is important?
Donbas was NEVER the objective of the Russian. I don't know what "paper" you read, but the ground situation I read is that it was not move, nor break out at all, suggesting that Russia is using Donbas region as blocking position. Which is basically to pin the Ukrainian troop already in Donbas, which is the only strategically smart decision Russia made during this whole war.
You don't even need to "Liberate" Donbas to achieve any of the Russian war goal. Again, Their war goal, as Putin put it is to demilitarize and denazify Ukraine, both of which involve a surgical strike to change the regime in Ukraine. Which mean Kyiv is key to both of them. You don't really fight a war with every inch of the soil to win a war. There is something in the military we called "Center of Gravity or COG" you take out the center of gravity, the entire country will fall.
en.wikipedia.org
And I am pretty sure the COG in this case is not in Donbas. Otherwise they would not invade the entire country, if they just want to liberate Donbas.