My problem is that any point I would have will be subjectively dealt with by the item designer(s).
But ok after rereading your sentence and this quote, that honestly I took some time to get entirely due to not being english speaking native, I'll rephrase
Is not having bard listed on this item an oversight ? there are a few hints from useable classes that lead me to think they should be able to wear this belt, cause all other plate classes + the other "roguish class" can, and bards would benefit from this item at least as well as the non-tank classes listed (cleric & rogue).
Thanks for pointing a few things that weren't right on my request.