Stagger in Raids

Didn't really see anything on this and didn't want to necro any threads from months ago -
Any reasoning why stagger wouldn't be allowed on raid bosses - the tank it's self is immune to tm manipulation.
But at this point for rancor - stagger on the main pig and rancor would be cool. Teebo, jyn , Thrawn basically wipe rancors tm away. Would it make Empire too well suited to the pit? Also if this was answered already please let me know. Thanks