I don't see any reason why anyone in the Kremlin would think it's justified to stage a coup (and all the loss of morale that brings for Russians troops seeing Russians kill each other) just so that they can purge some people Putin doesn't like anymore.
They could have done that anyway - Putin could have just straight up fired them, scapegoating them for the losses. If not one of those "he fell out of his bedroom window" cases that popped up a lot last year. Not like anyone would ask questions.
It makes no sense for Putin to instigate any of this. Or at least the risk-reward ratio makes no sense. Until something dramatic happens, I don't see any reason why this can't be seen as legitimate.
The Russians have been taking simply too many causalities. Even with the most conservative estimates (as per the Russians' own sources), they've had more causalities in 1 year of the Ukraine war than they did in 10 years of the Soviet-Afghan war!
Their supply chains, manpower, training, command-&-control, everything was at best patchy and ad-hoc. The so-called "reforms" of the Russian military in the last 2 decades were ultimately hollow and couldn't deliver a modern war machine. They were simply not prepared for a war this scale - like I said, everything after the failed Kiev airborne raid was simply the Russian Govt moving on autopilot.
There's more than enough reasons here to warrant a rebellion/coup attempt. It's another matter entirely if it will be successful or not though - and what kind of a Russia could emerge out the other side.
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What's for sure however is that the Ukrainians got themselves some much-needed breathing room. Their offensive wasn't going very well and they need time to hang back, resupply and re-assess their tactics. Well now they got exactly that. When they begin Round 2 of the offensive, it's very likely they'll be fighting a much more demoralized Russian force.