you won't run into threat issues if all you do is 123 threat in shield oats

the difficult comes in when you're trying to use sword oath at all with competent DPS.

essentially it's like a double tax on Paladins - their threat combo deals considerably less damage than the other tanks, along with them having no insane snap aggro (dark arts power slash, berserk MAN MODE burst opening), meaning that in spite of royal athority being 340 potency plus sword oath potentially giving comparable DPS on paper, in practice paladins are forced to repeatedly perform far more subpar threat combos than the other tanks, which in turn does less damage than the threat combos of the other two.