Scarlet Shocker exists on different shards as different ATs.
Scarlet Blaster isn't nearly as effective at sapping (or surviving) as Scarlet Sentinel. Partly I think that's because a Sentinel gets in the melee from very early on, and its survivability allows it to be in the fight for longer, whereas a Blaster benefits from having somebody to distract the mobs while delivering damage and/or secondary effects to be truly impactful.
As others have noted above, it's rare to get a team that focuses on sapping, so by the time any electric AT becomes effective, usually most mobs are dead or the fight has devolved to the players vs one or maybe two very tough AVs/EBs which are less vulnerable to sapping in the first place.
I'd also add, as an aside but important from the point of the Heroes game at least, that Sapping presents an opportunity to bring opponents to heel in a very non-lethal manner. Most of the game is balanced towards City of Heroes, but the logic of "I arrested him by smashing him several times in the face with a 12 foot long sword, your honor" does sometimes jar. Being able to neutralise somebody by completely removing their energy to resist seems like quite a good way to go about your business.