For PvE purposes. a tether neutralises a large target, makes them more susceptible to damage from 3 players for an extended period of time and controls mobs. Radiance allows you to throw grenades that pale in comparison to the amount of damage Shadowshot allows you to do in the same amount of time, while also only allowing the focus to be on one target at a time (e.g. you can throw grenades at whatever is threatening you, while Shadowshot can be used to take them out and at the same time, be safeguarding yourself from enemies in the immediate future)