Pikachu with light ball might hit harder, but it's speed isn't high enough to actually sweep in the majority of cases. And priority moves end any sweep super quickly.
Source: Experience using Light Ball Pikachu
Raising up a HA Raichu now, gotta breed it, then look at whether I want it physical or special. Raichu is generally better because of how balanced it is, but a pikachu with, let's say tailwind support is pretty strong. Depends on the tier, the battle and what circumstances the Pikachu/Raichu is in.
Never really been fond of pikachu' evolution line BUT.... I can't think o something better to deal with bulky waters.