The hardest part of the counteroffensive is the first part, they're pushing into the most heavily defended and fortified territory held by Russia. It will obviously be slow going, until eventually they break through and progress will happen more rapidly after that.

That was never going to happen. The lines have to strongly defended. But it is no assurance of defeat. It only increases the expense and time to recover. And once Ukrainians have some air force capabilities their combined arms offensive capabilities will be much greater.