[fbkaaipf] Bourgeoisie versus proletariat wages

The conventional narrative goes, the bourgeoisie put into place barriers against upward mobility of the proletariat.  This artificially keeps wages high among the bourgeoisie because of low labor supply.  It keeps wages artificially low among the proletariat because of high labor supply, and therefore keeps the cost of servant labor low for the bourgeoisie.

What is the nature of these barriers?  They are causing market failure in the labor market.

The barriers must be very secure because the proletariat are constantly probing and attacking it, constantly adapting, seeking to improve their lot in life.  Analogies: sea wall, or microorganisms against immune system.  I suspect inculcating identity is part of the system: it is something the proletariat (and people in general) cannot easily change.

Another problem with the conventional narrative is that the bourgeoisie are not a monolithic block.  They also employ other bourgeoisie.  The employer bourgeoisie compete against each other, seeking to minimize labor costs, so if they can expand the labor supply for a task formerly limited only to bourgeoisie, their labor costs will go down.  Thus the employer bourgeoisie will want to provide upwards mobility to the proletariat, so will work to dismantle barriers.  How do the barriers remain in place and not erode?