No USSR could not have been defeated - this is quite drastic to conclude but this is my motivation.
The Barbarossa plan incorporated by Hitler, was based on the vision that the USSR could be defeated by a fast operation and take Moscow prior to winter setting in. The communist regime would cave in and Germany would state the peace conditions and have lots of Lebensraum...
When I read about the execution of Barbarossa I guess the Germans did allright - even outperformed. So imho, the wehrmacht and generals are not to blame.
The USSR could have been defeated if Germany had planned otherwise - the conquest should be seen in a 2 years campaign. Or an earlier Barbarossa, which was unfavourable due to the size of the project. So a 2 years campaign should have been better. The most important error was that Hitler
neglected the impact of stranding in front of those big cities like Moscow and Leningrad. It would have been nice if panic took over the commies - but he didn't count of stranding on the outskirts and dealing with a counterattack on his spearheads ... that had been trained and operating to blitz trough this big country.
a relentlessly attack loosing momentum in front of a great strategic defensive structure - a mega city ! Supplied by a huge "Hinterland" that is

. This is not realistic ... even more if you look how large the front was - there were operations from Leningrad down to Sebastopoll - a huge operation with a huge front.
A little creativity would have solved the German problem if they had planned for 2 years - or had focused on the real targets Moscow and Leningrad. Suppose the Germans had focused on arriving at the gates of Moscow and Leningrad with an option to completely surround if possible. If not possible - they had to foresee a defensive situation and survive the fierce winter and take on Stalins winter offensive.
Also the naive Nazi stance on conquered territories - and possible allies - is likely to make the project totally unrealistic. The conquered Ukrainian people - and other minorities - could have been approached in a totally different way to aid the communist defeat and to guarantuee some stable satelitte after the hypothetical victory. The sympathy to aid the war against the communists wasn't really stimulated by the German approach ... and in the end the Germans where fighting everybody and everything.
The way Barborrassa was conceived leaves me with little doubt, this project was totally unrealistic.
Ironically Stalin saved his skin by launching his winter offensive. It was a tactical blunder but a strategic victory - giving the fact that Hitler was tempted to leave Moscow alone during the next year and given the fact that the Communist regime would cave in due to the political victory in Moscow...
If Hitler would have cut trough Northern USSR - divert resources from the Southern front to either enforce the Nothern drive - or to start earlier with Barbarossa - and instigate some sort of uprising in Ukraine - the communist regime would fall after Moscow and Leningrad were encircled. And if not - they could drive South the next year to liberate the Ukraine and claim the oil fields...