It's their doctrine modified based on their willingness to take and accept risk/losses.
What the Russians are doing in Ukraine doesn't really resemble their pre-war concept of how a war would be fought. They believed that wars would be very mobile with open fronts, and the dominant tactical action would be the meeting engagement. This hasn't materialized; what you see in Ukraine is a static and continuous front with complex trench systems and obstacle networks.
The Russians did have pre-war TTPs for fighting this type of engagement, which they refer to as a position of close contact. Broadly speaking, they are following some of these TTPs but not all of them seem to be workable.
I agree with the observation that they can't coordinate effectively at a higher level than companies, but it's not immediately clear why that should be the case. For all of their other faults, the Russians were usually acknowledged to do a good job of training their officers, but perhaps this is another of Russia's paper tigers. They have also sustained a huge number of officer casualties, so the surviving commanders might not be the best of the best.
I've mentioned elsewhere, as markppcli has here, that they are having trouble massing large volumes of soldiers in any one place. This would limit the ability to launch a larger attack for obvious reasons. It also frustrates the Russians, because the ultimate goal of Russian tactical doctrine is to allow mobile forces to get past the enemy and start moving towards operational objectives.
This is my own speculation, but I think there is an issue with Russian firepower as well. Their artillery does a lot of shooting, but it seems to have difficulty achieving enough mass to actually break through a solid defensive system. This is essential under their TTPs for fighting in positions of close contact - no attack will succeed unless the defenders can be thoroughly neutralized. Russian staff officers use mathematical tools to assist with planning, and in terms of firepower, they will calculate the number of guns and rounds needed to effectively suppress the defenders. I have a simplified version of one of these tools; assuming you want to break into a two-deep trench system on an 800m frontage, you would need at least two Bns of 152mm guns firing at least 48 rounds per gun of preparatory fire, and still more rounds to cover the approach to the objective and the assault itself. We just don't see much evidence of firepower being used on that scale. In fact, most of the times we see Russian artillery in drone footage, it's one or two guns or rocket launchers and not whole batteries.
Considering how many times I have seen a Russian attack fall apart after one or two vehicles hit an AT mine, they also seem to be short of good engineer support.
The Russians seem to have settled on a 1917-style "bite and hold" set of TTPs. Push forward some poorly trained soldiers to breach obstacles and get into the defensive system ("meat attacks," as they are sometimes called), then send forward some armoured vehicles and better-trained troops to exploit any successes. This won't lead to any big gains, but it will slowly capture ground and inflict casualties on the Ukrainians.
