I don't agree that you can minimise the disastrous impact of the non- aggression pact. (Nor does it seem to me that the error turns on failing to understand the special nature of fascism.) The point was that the Soviet leadership openly collaborated with the Nazis on a political level, giving credence to their regime and movement. Ilya Ehrenberg's memoirs make it quite clear that the pact went way beyond merely pragmatic avoidance of conflict to open collaboration.
Since the principal victims of the Nazis special measures were members of the KPD, this was particularly cynical. Strategically it was a disaster for the left, because it made them apologists for fascism.
In its own way, the subsequent policy of the 'People's Front' with the imperialist Churchill was just as foolish. It was the weakness of the Stalin leadership that they were incapable of making simply pragmatic deals (as Lenin did in exchanging grain for US technology) but felt the need to go further, justifying these tactical alliances politically.
Hence the false counterposition of 'peace-loving' and rapacious imperialisms - as if imperialism could ever be progressive. -- James Heartfield