Dull ranged?

Dull Ranged is an odd skill at best. It basically has the Casa Blanca+ effect, so I would probably say it could prove useful on tanks that are needed to take down units such as Reinhardt and B!Lyn. For example, Lyon makes amazing use of it to dispose of archers and daggers thanks to his legendary Raven tome. Overall, I'd say a tanky unit that can retaliate against the weapons that Dull Ranged affects will make great use of it if Vantage or QR does not fit (or in the case of QR, is in the Sacred Seal slot).

Its primary use is to counter blade tomes and honed units, I don't see it working at all on defense but you can use it offensively and see some success with it.

Someone who could utilize well would be a bulky enemy phase ranged unit like H!Jakob, W!Tharja, Hector, etc. Basically units that can bait with their bulk, nullify enemy bonuses and safely KO on the counter, so you'd want a QP seal with that.

However there are almost always better options for these units and B slot skills in general. Skills like vengeful fighter, sword breaker, vantage, etc. will be far more useful more often.

Probably an anti-blade tome user.

I'm considering giving it to my budget owl tome Katarina that I already use in AA to bait Ninos.