they didn’t “fight against fascism” until Germany invaded

Did you not read my comment? I specifically mentioned the Soviets being the only country in the world that meaningfully helped the antifascists in Spain with weapons, tanks, artillery and aviation, back in 1936, 3 years before the start of WW2 while all of western Europe was doing appeasement with the Nazis and "non-intervention" against fascism in my homeland.

Before the start of the war, the Soviets were famously trying to urge all of Europe against Fascism and in particular against Nazi Germany through mutual defense agreements. They signed one with Czechoslovakia together with France, which France refused to honour (see Munich Betrayal), which, and I quote Wikipedia: "The Soviet Union announced its willingness to come to Czechoslovakia's assistance, provided the Red Army would be able to cross Polish and Romanian territory; both countries refused.", again back in 1938, before any Fascist invasion of the Soviets. Furthermore, the USSR under the Litvinov doctrine sought after mutual defense agreements with Poland, France and England, to the point of offering to send ONE MILLION SOLDIERS to France (Archive mirror to bypass paywall) together with tanks, aviation and artillery to France on exchange for a mutual defense agreement, which France declined.

Looking into Soviet interwar policy, it's patently obvious that they were the strongest antifascist formation in Europe except possibly for the Spanish republicans during the Spanish civil war.

I’m also over-simplifying a bit in that I’m focusing mostly on leadership

My point stands though. Fascism was fought predominantly by Communist and Anarchist leadership. China against fascist Japan, Cuban revolutionaries against fascist dictator Batista, Spanish Republican government in the Spanish civil war... Whereas it was capitalist countries funding fascist coups all over the world such as that of Augusto Pinochet in Chile against socialdemocrat Allende, the Iranian coup against socialist-aligned Mosaddeq...