But then, they have also managed to seize a huge tract of territory in South and East Ukraine (in addition to what they seized in 2014).
They got most of it in the first couple of weeks. They gave up a lot of territory in the north after taking it initially. It's been a stalemate at best for the last two months. Considering Russian losses and Ukrainian weapons supply, this is not looking good for Putin.
If you are talking about North-Central Kharkiv, then yes. Russian troops withdraw from most of this region and Ukrainians hold a numerical advantage there. In the coming days, Ukrainian forces may regain some of the cities such as Lyptsi and Hoptivka. But at the same time, the Russians seems to be determined to hold cities on the eastern side of the river, such as Kupiansk and Vovchansk. And they have been advancing around the direction of Izyum. Russians are concentrating on Donbass as of now, and other regions are not their priority. That may change, once they capture the Sievierodonetsk-Lysychansk agglomeration and probably the Kramatorsk-Slavyansk agglomeration.