I guess the first step would be to incentivize having a group in the first place, for example making a way for "AoE" spells to be switched to "Group" spells.

Perhaps BC could actually have a stronger heal health / heal armor spell than the one currently there (as 100 health really isn't doing that many people a favor in the 10 meters around you). Then instead of affect those around you on the ground, it can affect all group members in a very large range. Stuff like this would actually give someone the distinct role of healer while also encouraging them to be in an actually "Group," and not just fighting side by side.