No, the outcome would have been far worse.

IF the left had formed a popular front, it would have been under Stalin, he was very clear about that. Trotsky had been exiled in 1929 and was assassinated — in Mexico — in 1940.
Stalin was involved in the 1936-39 Spanish Civil War.

The 1933 German election, which was basically fair, was arguably a choice between Hitler and Stalin and a lot of Germans (including German Jews) thought Hitler to be the lesser of the two evils.

Remember too that Hitler had been planning to start the war in 1942 or 1943, that Mussolini forced him to start it in 1939. So, arguably, the technologies that the Germans were working on — not just the atomic bomb but the V-2 rockets, guided missiles, jet engines and such, would have been completed, probably regardless of who was running Germany.

So there would have been an Iron Curtain extending to the English Channel, if not further. Stalin would have been in charge of all of that and Stalin already killed more people than Hitler did. So there would have been massive purge death tolls, particularly amongst the educated. What happened in Poland would have happened throughout Western Europe.
Look at what Stalin did to the Ukraine.

So then it would have just been the US opposing a true Fortress Europe and possibly one with nukes. That would not have ended well.

Extremism, on both the left and right, is what caused WWII — and Stalin was not a better option than Hitler.