although i havnt tanked any ex primals on my alt i can say in dungeons against a blm friend who is pushing m4s i can hold agro against him with my alt at 207-8 i forget exactly but def well under his ilvl and im only using a 210 weapon 230 chest and rest an even mix between 200-210.

i usually start with shield lob, fof, sheltron, halone combo mixing in ocgds like cos, spirits within and shield swipe which usuallly procs instantly because of sheltron. then cycle through goring and royal authority, repeat.
usually i stay shield oath in dungeons but after youve gone through those combos you could easily drop it and shouldnt have issues and even after the second halone combo you could drop it for royal authority and just monitor if you needed another halone.

really you shouldnt be having any issues unless your using str accs not realising the vit changes.