Sweeps in and of itself (plus Burning Light procs) will do more damage per cast than elemental weapon / force pulse. The channel time means that on a damage per second basis it ends up doing less, and pushes out refreshing of DoTs by a bit too.

If you run Combat Metrics and look at the combat log you can see what is happening more clearly. If you cast elemental weapon, weave a light attack, then hit some other skill, roughly a second will have passed. If you do the same with sweeps, more time will have elapsed. This means both that the attack itself has eaten more time but also that when lining up your other DoTs you go from being able to, say, refresh blockade near exactly 8s from previous cast, to refreshing it at 8.Xs, losing a bit of damage to the downtime. if you get that same effect across multiple DoTs it can add up.

There's also secondary effects in there. Sweeps is an Aedric ability so you get the passive which can be nice if not using the Aedric ultimate on the bar without Spear. It also increase the chance of proccing Burning Light. Finally, it does good cleave damage. Elemental weapon can apply status effects, which especially when solo / parsing against dummies can have a big impact because of concussed applying minor vulnerability. Elemental weapon can also trigger spell orbs if using frequently.

Long story short, it depends. For pure single target damage output elemental is likely the way to go. If the cleave or healing is valuable in a specific scenario or if you have no other Aedric ability on the bar, sweeps is likely to be the better choice.