Yes the Russians have learnt a lot albeit at the expense of effectiveness. By moving their logistics centres further from the frontlines they’ve made it harder for themselves to resupply their troops, also they have to move fuel/ammo/supplies a long way now via roads in slow moving convoys, thereby making it a turkey shoot for ukes with drone spotters and long range arty. So you could argue that the Ukes forced this on the Russians.
Those fixed defensive lines are formidable in so much as they have very deep minefields defended by well dug-in strongpoints. The Ukes need to eliminate the overwatch strongpoints and tgen that would enable their sappers to clear the minefields - however that’s proving difficult and it really is slowing them down.
I would say it’s a massive defensive line and it can’t be strong at all points / if the Ukes breakthrough in one place they really need to exploit the breach and pour forward with their heavy armour reserve. Starting to see this happen around Robotnye but not sure if it’s too late in the season for them to reach the Azov coast and split the Russian army in two.
War of attrition is an apt term for what’s happening now - it’s become a war of logistics - whoever masters that will prevail.