Maybe think about this...

They shouldn't do much damage when going tank. The problem is that they don't feel like they're sacrificing much damage when going tanky.

Against a group like that, Yasuo will want a QSS (and build into saber) and maybe even a maw. But his own mobility should be enough to help him avoid damage. Plus in teamfights he's supposed to rely on his frontline to protect and set up plays for him.

Ekko I feel would build some resistances, at the very least he'd get a visage for MR, health, and increased effectiveness for the heal on his ult. Beyond that he needs to focus on getting into the back line to take out the squishy carries.

And splitpushing is a thing. Not every comp has to teamfight.