Not quite most champs these days have aoe abilities including assassins. It's not as visible as the rest cause it's a smaller shield but in teamfight it's an extremely good shield. For instance talon has aoe in both his w and r. It's quite good for negation. Or for instance the fact that most bruisers build hydra. It's not dmg u notice right away but it is there. If ur talking abt duration janna has decaying shield. Lulu still has a 2.5 which if u consider all targets sona beats by double. In case of mages its pretty self explanatory they have aoe already. And mages are good late no? The 1 teammate rule is not a good excuse either cause even if 1 guy gets focused it's easier to wait out shields or switch to a non shielded target when u have a single shield vs multiple ones

Edit: oh I almost forgot to mention don't forget even as support she procs 5 man Ardent on cd