I wish to suggest a new feat that I think would gap the worst AC disparity between two-handing and sword-and-board without making the former too powerful. Taking inspiration from the Ki Barrier feat, I suggest adding a general feat that grants HARD constitution modifier as Shield AC.
This would provide Shield AC in the range of +2 to +5 for most builds, on par with the air stance of Elemental Avatar or the passive AC bonus of Ki Barrier on melee clerics and shamans. Less than or on par with any sword-and-board combination, but enough to make a difference. If necessary it could be capped at +5 to account for EDR bards.