Recent update changed One For All to gain an incrementing buff that applies damage reduction to the group instead of mitigations.

However, this update also changed the way this buff increments base on the type of allies near you.

The buff is still raid-wide, meaning any ally, regardless of group, will get the buff.
However, the buff only gets stronger if you apply it to ally from your group only, meaning that while other allies get the buff, it will not be stronger.

This generally isn't that big of a change for non-raid scenarios though.
Unsure if WAI or not, just putting info out there.