imo set items are a feature more biased towards multiplayer because they encourage trading. sure a lot of set items are nice even without any extra set bonuses, but since you find a lot of different pieces a long time before you complete any one full set that is actually useful to you it makes sense to trade for it, because on sp/selffound mp usually once you complete your set, youre already fully equipped with sacred uniques and crafts and rws that are good enough to finish everything easily.
so what some of the speakers before me said is true, either trade for it or think of alternatives to the set, because the only other option is farming for an indefinite amount of time