This is a feature, not a bug. This is how a system of checks and balances works in authoritarian countries - the entire security apparatus is duplicated several times over lest one agency becomes too powerful or indispensable. KGB/Ministry of the Interior/Military kept each other in check for much of the later part of the Soviet Union's existence.
Russia also has had at least three armed forces up until recently, the normal one, the Rosgvardia, and the PMC complex including Wagner. All of them have had rather serious equipment, for example Wagner had tanks, artillery, they even had their own air defence like Pantsir and their own aviation.
Running an oppressive, murderous regime sometimes requires crazy solutions.
> “They think—what do they think? That we’re important officials?”
> “No. Of course not. They know we are only pretending that.”
> “Then what—”
> “But they cannot be sure. We might be important officials. But most of them think we are secret police.”
> “But how do you know there are secret police?”
> Benito looked very sad. “Allen, there have to be. You cannot run a bureaucratic state without them. Come.”
-- Inferno, by Jerry Pournelle and Larry Niven
I can easily think plenty of countries around the world where security and intelligence duties are often duplicated and overlap.