I'm only going to talk about InFamous 1, InFamous 2, and a bit of Second Son but excluding First Light and the DLC Festival of Blood as they don't hold truly significant relevance to the Ray Sphere.
What the Ray Sphere Is?
I honestly found the lack of it in the games after InFamous 2 extremely underwhelming as it was what kick-started the entire series and the activation of the first known Conduits like Kessler alongside Cole MacGrath. While I understand that all events of Infamous: Second Son follows the events of the good ending which involves using the Ray-Field Inhibitor (RFI) to globally eliminate all living possible conduits, but then gave way to Conduits being just born with it like some Avatar with bending just honestly felt so bland to me. What made the games more enjoyable was how every backstory of Kessler, Cole MacGrath, Lucy Kuo, Nix, Joseph Bertrand, and John White or the Beast was their different experiences from the Ray Sphere.
Joseph Bertrand basically forced a ring of outcasts with him at the center, outcasts like swamp dwellers and homeless people just trying to get by. He would then activate it and vaporize everyone around him except Nix, in result it would activate both his and Nix's conduit gene. The ability to become a Conduit wasn't just something one could activate, you needed a Ray Sphere which required an immense amount of resources and that isn't even including the high amount of bystanders needed to be close by. It could only be built by The First Sons as it was led by the knowledge that only Kessler possessed having witheld knowledge that nobody else could obtain but him. The idea of a Conduit held high value because it was only a 1 in a 1,000,000 chance and could only be activated by a Ray Sphere which was impossible to acquire unless you were a member of The First Sons like Dr. Wolfe, you were Kessler himself or gifted by him like Cole MacGrath, or you held immense resources and power like Russell Bertrand who held connections with power players and had two entire cities in your pocket (Flood Town and New Marais) & your own militia and ability to enable projects like the one that created the Vermaak 88 or Ice Conduits.
While yes, Second Son takes place after the Cole MacGrath uses the RFI leading to the deaths of all living conduits globally but also basically giving a greenlight to all future conduits like Delsin Rowe, Abigail Walker, and Eugene Sims who just needed to basically be under a lot of stress to cause it to activate, all of this meant that it wasn't as non-existent anymore and wasn't as special as it used to be. Prior to the RFI, it was only a 1 in a 1,000,000 chance and even being that one lucky person didn't mean it was any easier as the Ray Sphere was completely unobtainable unless you held connections with power players, or a member of The First Sons, or Kessler himself, which was less than 10% of the entire population including those with the Conduit genes.
In Second Son, it was 10x easier now. While you still had to be he lucky person to hold a conduit gene, you just needed to be under heavy stress as the RFI basically eliminated the entire hefty and heavy-effort process to activate it, the mechanical part. I'm not saying that being under heavy stress isn't a heavy process, I've gone through a lot of experiences that are worse than what Eugene had to go through with the bullying, but it was easier, again I'm not saying that being under the stress they went through in Second Son wasn't jack. It simply wasn't as special and unique as it used to be. Yes, it was probably still less than 30% in Second Son, but there was now probably greater than 10 conduits we don't know of as Second Son only takes place in Seattle when we know at the ending of InFamous 2 that it was global and that several reports from places in the opposite side of the world from New Marais was experiencing its effects.
I honestly think that they shouldn't take a few steps back but should pick back up and re-use the idea of the Ray Sphere or something of equivalence. While the feeling of being unique is definitely one of the things that come from my desire for this type of plot, its also that the effort needed felt more significant and heavy. We witnessed ourselves and not through cutscenes what happens after the Ray Sphere is utilized by Cole MacGrath in InFamous 1. The blast destroyed everyone at a 3-block radius with him at its center, causing an entire district to basically experience a mini-nuke and forcing Empire City to go into full-government lockdown. We had to go through ourselves and venture through the rubble caused by the Ray Sphere of Cole. John White tells us clearly how his Ray Sphere literally tore him apart, not only his limbs but every single atom/molecule in his body was teared apart from one another and how the effort that he needed to pull himself back together couldn't even be measured by words.
In Second Son, all we get are cutscenes. The closest we got to it was the explosion at the Akomish Longhouse and it doesn't even topple the building, just causes an internal fire. It was all basically just cutscenes and while the stress they experienced isn't nothing, we don't experience it ourselves and its so difficult to feel a strong connection to the character's pasts.
I just think the Ray Sphere or something similar to it not existing in Second Son honestly made me not enjoy it as much as InFamous 1 and 2 and I think a lot will agree with me on this, if you played the first two before Second Son. I've only met people who enjoyed InFamous: Second Son and believed it to be better than the first two, when they played Second Son first and never or only played 1 and 2 after, so I could be missing something with this paragraph.