TheSword
Legend
And without magic items the fighter has a 21 AC at best versus a +18 to hit, and their highest save is a also a +11, only their's is Con, which is going to half damage anyways most of the time.
This is the problem with this kind of white room theorizing, because 20th level characters do have a careers worth of magic items which for a fighter is likely to include a magic sword, magic armour and magic shield if needed.
Shield mastery, Resilient, Indomitable all improve saves with very little cost.