Aside from the grotesque and abhorrence of the act, the Wagner group is displaying another problem for Putin: they seem to be slipping out of his control.
The Russian government, when asked about the video and execution, said 'its not our business'. Wagner group have their own fighter aircraft operating in Ukraine, it's arguable about how much they depend on the logistics of the Russian Army, and how much the Russian army depends on the Wagner group...
Putin has set these groups up - as well at the Byzantine plethora of different ministries each with their own armies - as a way both to do his dirty work, and to provide his government with multiple, and mutually suspicious, layers of protection, but what's been created is beginning to look rather like the 'over mighty subjects' of the English medieval period. The Chesters, the Gloucesters, the de Montfords, the Mortimers, the Nevilles, the Percies, the Dudleys, the Norfolks....