Non-duplication rule “an amount cannot be treated as W-2 wages by more than one trade or business”. I suggest here the key is a written agreement between the management company and client, which for consistency must be followed each year after.

Why would the management company give up their right to a QBI item?

FWIW - I'm siding with the Nos on the Managment company employee wages. Right now I'm working on a slew of RE partnerships, all of whom have management companies. The managment companies all have employees.  I think it is a stretch to say the management company's employees are employees of the RE partnerships. The management company cah hire and fire them, move them to different properties, control their hours, tell them what to do, etc. The RE partnership cannot.

Now when I get to my partnerships and corporations that use PEOs, I'm using those wages.