>like all Marxist theories, falls apart when applied to reality.

Some but not all. This one certainly doesn't fall apart.

>Saying things like the homeless 'serve a function' for corporations to 'keep down wages and agitation' only makes a lick of sense if you see 'corporations' as one giant agent which rules society

Cohesive power blocs often come together to act as as a unified political agent when they have shared interests.

Two good institutional examples of corporate power blocs in the US are Cato and the AEI. Many of their members compete for market share, but they joined forces to gain political representation together to have their interests as a whole represented.

Actually according to Marxism capital doesn't have to collude, there need not be any conspiracy, holding down the workers is the natural conclusion of capitalism.

This is like saying systematic discrimination doesn't exist because the hegemonic group does not have a single organization deliberately applying discrimination.