Are the Russians claiming they are shooting their own wounded? I haven't heard that
I think the Russians are underperforming and the Ukrainians are overperforming. It is hard to really know what is going on, but I think the Ukrainians are more using infantry units with anti-tank weapons to hit and run. I don't know if the Ukrainians are letting the tank and mechanized units pass and then hit their supplies.
The longer the Ukrainians can fighting back and causes a lot of casualties they may pull this off, but that depends on how much more the Russians can take the cost of the war. The sanctions and the casualties can make them to react. It also depends on if Putin mysteriously and suddenly dies. He can't back down, but how long can the other Russians in the government live with this.
I think I said something about giving the Ukrainians systems that can deal with the Russian artillery. I would try to use their Turkish UAV's against their artillery if I were an Ukrainian officer. Another option would be to try to hit the Russian railroad hubs in southern Russia. A lot of their supplies are going on railroads and if the Ukrainians can hit where they unload their supply trains and load it on trucks would worsen the Russian logistical problems.