How was the compromise of 1850 even a compromise? What did the southerners get equal in value to California being added as a free state?

No agreement of that sort can ever be exactly 'equal' in all its provisions, once you start taking into account land areas of the relevant parts, relative population numbers in each part, relative proportion of whites to blacks in each part, different types of agriculture in each part, etc, etc.

They got to keep Texas as a slave state, with its debt (which was substantial) being forgiven by the federal government.

At the time, Texas' debt was a much bigger deal than California's statehood.

Even more, and worse, it forced people in free states to help slave owners recover their "property."

Two gallons of the finest Kentucky sippin' whisky, brewed by the legendary Mike "Mountain Mike" McDongle himself. Even a pint of that potent brew was equal in value to California being added as a free state, never mind two gallons!