Radial Sweep needs help. Here is why:
The Fighter's Guild passives are outperforming all other non-class skill trees. These passives incentivise players to make room in their skill bars for at least one skill in order to reap the benefits of the passives. The most simple choice is to slot the ultimate itself, to no detriment to their damage output. DB offers an Area of Effect stun and hitbox, increasing the damage potential and group play of players.
The issue with DB being relatively cheap to cast is that it is not so much more expensive than Radial Sweep. Seasoned Templars will slot DB over RS every single time because 1) Flawless DB increases weapon and spell damage by 300 on cast, 2) Dawnbreaker of Smiting has an on-command stun that can be combo'd with Backlash, and 3) RS is just a nerf gun representation of DB. RS only does comparable damage to one target, DB treats everyone equally. DB does 10% more damage for being a FG ability, add another 10% if you hit werewolves or vampires.
Radial Sweep is utterly useless because it has a cheap cost, thus, to keep it balanced the performance must be reduced. You get what you pay for. This is unlike another cheap ultimate: Incapacitating Strike. Let us compare the two: RS has a much lower tooltip and a somewhat mediocre Damage Over Time. Incap has tooltips akin to more expensive ones while also granting a 20% damage bonus to follow up attacks. Radial Sweep's damage is embarassing. The new changes to RS extending the DoT duration to 10 seconds is utterly useless for PvP. Burst kills, DoTs don't. There is a reason DoT bombers don't exist.
In summary, Radial Sweep is weak because it has a low cost. Don't even get me started on Empowering Sweep. The solution: Raise Crescent Sweep's (PvP morph) cost. Remove the DoT, make it last 12 seconds and add an explosion every 6 seconds. Alternatively, return the DoT duration to 6 seconds and add a stun at the end of the DoT.
This is all from a PvP perspective pertaining to small-scale combat (1-4 people in each