Russia does not seek to add Donbas to its formal territory (like it did with Crimea) but rather seeks to station soldiers and allied locals there to destabilize Ukrainian territory to make it impossible for Ukraine to join or strongly ally with NATO. NATO is somewhat selfish and won't admit members like Georgia and Ukraine with active territorial disputes with Russia. In the long run, Russia wouldn't mind if Donbas residents voted in Ukrainian elections as long as they voted for candidates under the control of Russia, putting Ukraine back under Russia's sphere of influence (like Belarus is today).a) if Russia is as invincible as some would have you believe then why have its regular forces been fixed in the Donbass conflict for so many years and against a supposedly inferior Ukrainian foe?
Let me list some perceived advantages of Russian ground forces over NATO ground forces in a straight up fight. This doesn't mean that Russia is starting a major war soon, but this thread is mostly about getting the British Army to a place where it can fight the Russians.
1. The entire Russian ground forces are optimized to fight NATO. This is more or less the only task they train for.
2. Russian has thousands of main battle tanks. MBTs appear in all formations, including mechanized infantry formations. The MBTs are fairly upgraded with high protection levels and guns and ammunition with high penetration levels. The 1980s T-80U was a high end machine then with an estimated 780mm RHA equivalent protection against kinetic energy (using ERA). I have seen figures for the 1990s Challenger 2 of 600mm and similarly for the base model M1A2 (although it has been upgraded three times since). Most Russian tanks have been upgraded within the last ten years and have added more protection. Meanwhile, I am seeing figures like 1000mm RHA or more for how much the most modern Russian APFSDS on in service tanks can penetrate.
3. The British Army has been focused on Afghanistan and Iraq for the last twenty years and has gotten rid of all but two of its main battle tank regiments.
4. Russia has massive amounts of artillery throughout its formations and keeps buying more. Russia has tube artillery, MLRS, and more. This thread has gotten into some modern Russian artillery systems and how they seem to outclass legacy NATO systems. Russia has exotic munitions like thermobaric and cluster munitions that Britain has banned or won't buy. Russia also has large quantities of artillery enablers, like counter battery radar. The British Army might have a few sets of counter battery radar somewhere.
5. Russia has plenty of intermediate range missiles for deep strike.
6. While I doubt they compete with the latest Apaches, Russia has plenty of helicopters.
7. All Russian brigades have large EW units in them. There are also sorts of battlefield EW vehicles that the UK lacks.
8. Ground based air defense for all ranges is about the best in the world in Russia, perhaps excluding ballistic missile defense.
9. Russian light forces are no slouches and will be engaging in disruption in the NATO rear.
10. Russia has automatic minelayers and similar equipment that NATO has divested. Britain banned most mines in 1997.
11. Russian vehicles are more amphibious than NATO ones and Russia has many more bridgelaying systems than NATO does.
12. Every Russian brigade and possibly battalion has a large CBRN unit, something that barely exists in most NATO armies. There should be plenty of CBRN ammunition if the artillery needs it.
13. Russia seems up to speed on drone use.
14. This thread has mentioned heavy equipment transporters. I imagine Russia has tons more HETs than NATO armies do.
In summary, Russia took over the high-end warfighting capabilities of the Soviet Union and has been upgrading them over the twenty years of Putin's rule. NATO has all about saving money for non-defense spending and conveniently emphasizing less expensive counterinsurgency operations.
The main weaknesses of the Russian ground forces are their reliance on conscripts and their general corruption and bureaucracy. But some of those corruption and bureaucracy issues would be put to the side in a shooting war. The conscript quality is better than in the Soviet era as Russia has few Central Asian conscripts for whom Russian is not their native language!
The main threat to the Russian ground forces, after slogging through Poland's ground forces, is the US Air Force. I am not so sure how the USAF would fight such a war.