RAF mass destructive firepower.
I still think the range and power projection of the RAF would have been the decisive factor in 1946 against Russian forces in grinding them.
Russian tank forces would have had little in the way of supporting fighter aircraft cover of a standard to match the RAF Fighter Command either. Perhaps they (the tanks) could have got to the North Sea but once there they would have taken a terrible pounding from the RAF and this would have continued for a considerable period.
The strain of trying to endure that air assault, hold and rebuild Europe, keep an army happy that had endured, what 5 years of hell(?), it would have been too much for them. Perhaps they would even have entirely collapsed.
Harris would then have been seen to be right.
Additionally we would also have recalled a very capable RN and FAA into the North Sea. Their own interdiction against the Russian armoured forces would have been considerable...
We would have just had to keep on fighting and fighting.....
It truly is a most horrible thought mind, how it would have gone.