As much as the Wagnerites prove to be more efficient than the regulars, the reply is common to most "warlord"-style formations during trying times: they're more flexible, they have more motivated officers and troops, they're easier to employ and "spend", their command and logistics function more on personal charisma and connections than standard bureaucracy.... Wagner isn't particularly special in this regard, history is littered with similar formations (from the Tiger Forces of Syrian heritage to some of the SS formations or the X MAS of WW2 fame).
The bad thing is, they're a symptom of .... problems. When your most efficient troops are those that aren't managed directly by the State this means the State has failed to properly train, equip and tard wrangle the Army. This means personal politics become even more important than battlefield performance, and often cause infighting. Recruit drain and resource drain as more successful warlord groups get prioritized above regulars and recruits flock to them. Warlord armies are sometimes efficient and I do not honestly believe that history repeats itself, but they're often the sign of something not working as it should.