Russians BTGs were a failure, an attempt to create a hyper-flexible swiss army knife for offensive + defensive + occupation activities, which then fell apart when they faced peer-level resistance from the Ukranians.
The BTGs were mostly Infantry and Artillery, supplemented with Tanks and specialty assets. Heavy losses in one of the main three segment made the rest of the BTG mostly or entirely combat-ineffective. And that's basically what happened -- the infantry and tanks died, and artillery was relatively untouched, which led to Russia sending convicts (Storm-Z) to find targets for the (still remaining, quite numerous) artillery.
They did not have real, integrated logistics and heavy engineering units on the BTG level (though they do have combat engineers / sappers). What supply units they do have are limited, and they are dependent on higher level replenishment organizations for operations lasting longer than 6 days. Those replenishment orgs inevitably got bombed by the AFU, so the BTGs rapidly ran out of gas and ammo, even when rocking a full TO&E.
They did have integrated EW and HUMINT capabilities, with the EW being particularly potent; Russian EW is still very good, even on the BTG level. The downside of these, though, is that they are a swiss army knife; small enough to be useful, but not big enough to be ideal (and withstand casualties), and it forces a busy commander to divide their attention in ways that a larger org may not.