The number of Russians KIA is a controversial figure. Not all casualties on the Russian side are equal. Wagner is staffed by prisoners and professional mercenaries and the lives of Wagner troops does not matter. The 80% casualty figure seems credible, given the big deal made during Wagner demobilization ceremonies. One would think there would be a lot more Wagnerites at these events. Furthermore, we've read accounts that Wagner has difficulty recruiting in prisons, because prisoners found out how deadly six months in Bakhmut can be. Russia used prisoners to attack Bakhmut because their lives don't count. This is Russian state policy: let the weak die. Prisoners may be a combination of hardened criminals and drug addicts, but Russia's hard-line anti-drug policy suggests the lives of both categories are worth zero. Compare that to the mothers of drafted soldiers who pushed for Putin to end the war in Chechnya, or the families of the sailors of the Kursk submarine. Russia cannot afford to lose Slavic young men and has been revising its doctrine to conserve their lives... even at the expense of LDPR and Chechen lives. Both might be on the same side, but only the Slavic Russians form the political constituency of the Russian government. LDPR soldiers are fighting because all fighting age men are already treated like combatants. Since they are not integrated into the Russian MOD armed forces, they don't count. And Chechens are the new Cossacks: universally feared and used as a weapon by the state against other ethnicities. Combat is part of their social contract with the state.
Russia came by this policy through hardship and bankruptcy. The post-Soviet social state collapsed. We saw how Putin cut the pensions of Soviet workers and social services were slashed, then eradicated. Drug addiction, alcoholism, murder, suicide, accidents, and disease killed Russians in the 1990s at the same scale as major wars. Russia's population dropped. It was able to use the financial surplus to build a reserve base to finance its current international ambitions. If that money was spent on social problems, they'd have no spare cash. And currently, the Russian government sees no interest in changing its social policy.
Since the modern economy runs on the smartest 20% of society, and 33% that have a work ethic, and those with miscellaneous virtues (like thriftiness, bravery, or community values)(don't forget that these categories overlap so we're probably not even looking at a majority), everyone else is just consuming resources that could go to the rest of society. The official Russian attitude is that these lives don't matter and that society will carry on just the same without them. We see this in the Russian financial allocations. There is a minimal safety net. Additional funds for drug addiction, social work, and efforts to rehabilitate the anti-social personality are virtually nil there. This reflects values. Hit rock bottom and maybe save yourself. Nobody else is going to do it for you. Society runs on an assembly line and if you're a misfit toy, go die and stop being a burden to everybody else. Sounds cruel to Californian ears, but so does war. Therefore, it seems likely that when using Russian MOD figures to calculate casualties, we should keep in mind that the number of Wagner and LDPR casualties could be much higher and even many times higher.
Aleks at Black Mountain Analysis has some insights into the latest public moves by Prigozhin here:
https://bmanalysis.substack.com/p/opinion-piece
They do not conflict with your premise, stated here.