Check the numbers on the Soviets at in 1941-43. They had a numerical advantage in every category on the Eastern Front from at least Autumn 1941 on. That's not even counting anything the Brits added to the equation.
Also don't forget the RAF actually had more single engine fighters than the Luftwaffe by the end of the BoB due in large part to purchases in the US, not to mention later, yet still got smashed on the Channel Front from 1941-42 (in 1941 the RAF lost 849 fighters not counting bomber losses vs 183 Luftwaffe fighters):
https://books.google.com/books?id=UmwwBwAAQBAJ&pg=PA239&lpg=PA239&dq=raf+circus+1942&source=bl&ots=2QtDIldFIq&sig=kPqJmrYc2cA4uGRJPlymZJxp6JM&hl=en&sa=X&ved=2ahUKEwiB2c_whdneAhXim-AKHVfWDmAQ6AEwD3oECBoQAQ#v=onepage&q=raf circus 1942&f=false
Ever hear of something called FORCE MULTIPLIERS?
--training
--logistics
--experience
--air support
--weapons effectiveness.
--defense
--competence at all levels in how to do the basics from Ivan to Zhukov?
The Russians only had two advantages; they were on defense and the Germans were not paying attention to logistics as they ought 1941-1943.
Let's take an excuse that some people have for German failure: the T-34 surprise just prior to Barbarossa.
From the numbers I can find, when the Germans invade, the Russians have about 1,000 T-34/76s available in 5 tank corps. The PROBLEM is that is that these tanks were new issue, with the short barrel 76 (Thank you Grigory Kulik!) that was woefully inaccurate, had a defective AP round and the tank crews had less than 10 hours in machines.
If the Russians were going to stop the Germans at the tactical small unit level with tanks; it would be in T-26s and BTs. Those were tissue paper to existing German weapons. The PZKWIII even with the short barrel 50 mm was perfectly happy to punch holes in that junk. Add that the panzer crews knew how to fight their machines well.
Russian Infantry at the squad and platoon level was armed with junk that their grandfathers threw away as useless in the Russo Japanese war. Now the Mosni-Nagant was/is quite a good rifle, but you had to have good bullets to make it work. What did the Russians not have?
Back to the T-34/76. Have you been inside one? Ergonomic disaster. Commander station, loader's position, I've seen WW II French tanks that were better laid out. Anyway, the T-34/85 is a LOT better because the Russians learned from combat what sucked in the T-34/76 and fixed it. Bigger better gun is what most people notice, but it is the improved ergonomics and RADIOS that make Soviet tank crews much more effective. That happens mostly after Kursk.
Now in 1943, the Russians come out with an improved infantry machine gun, the T-34/85, arm their assault troops with the PPsh 41 and PPS 43, and start rolling out Sturmoviks and Yaks, but the things that really make it all work, is that they rationalize their logistics chain (American experts imported help with technical advice and know-how as well as locomotives and rolling stock and railroad track laying and bedding equipment and trucks, never forget all those trucks!.), the STAVKA has managed to sideline the political officers and muzzle Stalin (temporarily), and Sergeant Ivan since he is still alive can teach Recruit Boris how to fight Germans. It has to be Ivan because all those brand new Lieutenant Pushkins are still idiots. The sooner Ivan can get the Germans to kill those know it alls, the better. Anyway, field grades, OJT, division grades now pay attention to feeding the troops and making sure that the ammunition is distributed and there is some TRAINING.
It pays off. Tactical proficiency between Felix and Ivan at the soldier level narrows to the point where it is about 1.1 to 1 and that is when numbers finally BITE. That does not actually happen until January 1944.