@Tactical-Ochoa Very detailed post with some great points all round.
100% agree with Albedo. With regards to Eon I certainly believe that he would've been more effective if they'd actually delved into his backstory a bit more. To show us how he became that way, and to highlight just how much he contrasts with Ben. There were probably opportunities in Omniverse to do so but they didn't really capitalise on it, potentially out of fear of making the story too dark. Actually I think that he would've made a far more effective villain than Maltruant if they'd done so.
The differences between Ben and Kevin also really show "nature vs nurture" at its fullest. Ben and Kevin share a lot of similarities as people, but Kevin represents the path which Ben could've gone down if he hadn't grown up around such good people with a proper sense of right and wrong. Kevin's backstory is honestly quite tragic , he was born with abilities which he didn't want and his family rejected him and chucked him out of the house for being a freak.He's someone whom you can understand but yet someone who you cannot forgive at the same time. "Kevin 11" is one of the darkest and most thought provoking episodes of the original series for this reason. Heck, even when they do have to work together in "Grudge Match", at the end of the episode Kevin saves Ben's life, but only because he wanted the pleasure of killing Ben himself. If that doesn't give out Joker or Green Goblin vibes then I don't know what does.
A lot of people defend his redemption in Alien Force because they say that Ben is always willing to forgive and give people another chance, and that with Kevin maturing he realised the error of his ways. People say that Ben and Gwen teamed up with him at first out of absolute necessity because he had alien tech, knowledge of Forever Knight operations and trades , and then this eventually it grew into mutual trust. UAF then retconned him into a half-Osmosian, with his Osmosian father being Max's Plumber partner (and if this is true then Max is an utter jerk for never reaching out to his partner's son at all in the original series. Not to mention how the space Plumbers are another retcon by themselves). Then they came out with an explanation that absorbing energy drove Osmosians insane beyond their control, but was completely reversible. This was meant to be a way of justifying Kevin's redemption but it just meant that he had no responsibility put on him for his actions. Kevin was clearly the writers' favourite character in UAF and they put so much effort into further developing his redemption story when it really did not fit his character and setup at all. People - especially teenagers - do change over time. And UAF Kevin by himself is a very entertaining character who is given a lot of depth. Just...why did Kevin have to get a redemption out of all characters? Someone like Charmcaster was far more deserving of making the transition to becoming good.
Don't get me started on Gwevin. I'm not into shipping at all but the Gwevin ship was unbelievably rushed and not thought out at all. It really made no sense otherwise given that neither showed any kind of care towards each other in the original series, and then all of a sudden in Alien Force we have these cringey romance moments in the very first episode? Isn't Gwen meant to be smart? I think she'd know better than to trust someone whom she last encountered like this. What a loving, caring couple they'll be in the future, right?.
Apparently Dwayne Mcduffie actually planned for Kevin to be going through an anti-hero/vigilante arc in the background which would've been better, and for Cooper to be the third member of the trio, but Kevin being good was mandated by CN for reasons which we'll never know...
I don't think that Kevin has to be a full blown villain. I think he'd probably also work well as someone who isn't definitely good or evil and walking the fine between. I think that him going through something similar to what Charmcaster did in UAF and OV would be far more fitting. The most important thing however is that he acts as a dark mirror image to Ben. That's what made him a good character in the original series and I think that he'd be effective as a means to show how Ben grows as a character, especially if he gets his own character arcs to parallel Ben's. His conflicts with Ben will always be personal as opposed to the vast majority of other villains. I believe that Ben would keep trying to give him chances and I can see them teaming up very temporarily in pursuit of a common goal (eg. stopping the Highbreed) but Kevin would be more likely to ditch them/backstab them when he gets the chance. I actually think that Michael Morningstar (with some tweaks) is actually a pretty good representation of whom Kevin is, what with him being addicted to absorbing energy and not giving a damn about anyone else other than himself.
I will say that I think that reboot Kevin going through a good guy transition similar to Alien Force's could work, as could his bond with Ben and Gwen given that he didn't try to hunt them down or kill them for no reason. But it does not work one bit for Original Series Kevin.