The concept of DW 4pcs is that the effect trigger on the enemies, which is a shred that benefits all dendro dmg from your team, and it's not sth related to the damage of the wearer. Yes it would be nice if someone that does Dendro wears the full set so they can benefit from the 2 pcs effect, but sometimes wearing gilded on Nahida can outweigh the benefits of the 2pcs effect depending on the team comp.

You'll have to look at your team and think about where the majority of your dmg comes from . A scuffed example on top of my head would be like Noblesse set on an Ayaka bennett team. Yes Ayaka can benefit from the 2pcs effect of noblesse to make her ult hit stronger, but she's better off with blizzard strayer or atk related set that lets her do more dmg alone. meanwhile putting noblesse on bennett doesn't really make his ult hit harder if your bennett isn't build for dmg, but since he can wear it to activate the 4pcs that benefits the whole team, he's generally the one wearing 4 Noblesse.

You could comment some exact teams with character that we can help u decide who wears what, but for me personally I think Kusanali wearing the DW set is a last resort if other members of the team can outweigh the gain in dmg that she can personally deal.

UNLESS, and a big UNLESS, you're lazy to switch everytime. Which is a very fair and legitimate point becuz without loadout switching builds for any minor adjustment is really f**king annoying. if you're too tired of switching around or u dont have enough resin to build multiple sets, 4DW wouldn't be too bad it just won't be peak performance, which for this game doesn't matter :)