"letting Germans bleed out across Europe"

How much exactly did they "bleed" before starting war with the USSR? AFAIK they mostly took countries intact with low to none losses.

They took 50-90% (depending on the source) of their total losses fighting the Soviets.

It's generally agreed upon that Germany started the war with Russia and that they lost because of the resources their Eastern front required.

Yes. But first Germany and the Soviet Union jointly kicked off World War II.

"This is not a peace. It is an armistice for twenty years."

"...the greatest villainy of the century"

"Peace for Our Time"

The USSR didn't "ally" with Germany. They signed a non-aggression treaty, which basically meant they agreed to not attack each other while partitioning weaker states. Which is similar to what the western powers did together with Germany at the Munich agreement (which didn't include the USSR).

They did ally with Nazi Germany.

Non-allied states are not performing joint military invasions or provide military support to each other in ongoing war.

80% of German casualties were on the Eastern Front. USSR fought Nazi Germany head on, matching its strength with human resources prior to 1942, and outmatching it technologically past 1942. Submachine guns for every infantryman, a large amounts of good tanks and artillery (including rocket artillery) and passable airplanes led USSR to victory.