agro is not taunt per say as they are meaning on bubblers...- if you softcap defenses for everyone on your team it becomes possible to pull a lot of mobs on top of the team, which expands the 16 mob agro cap further to a "per person" and spreds it to others. big swaths hit by forcebubble, then the bubbler would drag it back to team and rebuff shields usualy will distribute the agro to rest.
its a big reason behind the outcry to leave force bubble alone - that power is the biggest mobile agro tool there is, can grab a lot.