When talking about the distinction between Simon Petrikov and the Ice King, it’s important to remember that originally, the Crown wasn’t trying to turn Simon into Ice King -
It was trying to turn him into this guy.
At the time, the Ice Crown - or rather the Wishing Crown - was programmed with Gunther’s wish to become Evergreen. So everything related to making the current wearer like Evergreen is a very direct result of the Crown’s Magic. The physical changes -
And the obsession with the name ‘Gunther’ -
And maybe some of the irritability and anger issues -
That is something the Crown is very directly forcing unto its current wielder.
Ice King, personality-wise, was not much like Evergreen at all, or even like Gunther's view of him. And Ice Finn of the Farmworld Universe was also pretty different from the both of them.
At the time, I remember people assumed Ice Finn’s behavior is more indicative of what the Crown is actually trying to do with its wielders. That Ice King is so different because of Simon’s subconscious resistance against the Crown - while Finn’s much younger and dumber brain is a lot susceptible to the Curse’s influence to become some sort of mad world-conquering emperor of ice and snow.
But, with the context of the Crown’s actual backstory. That doesn’t seem very likely anymore. I think what’s actually happening there is that the Crown is just trying to make its wielder an Ice Wizard on par with Evergreen (who was the Actual Goddam Ice Elemental) and that means pumping the wielder’s brain so full of Magic, Madness and Sadness to a level that is bound to overwhelm anyone.
And Simon’s and Farmworld Finn’s very different behaviors after putting on the crown is indicative, more than anything, of how their psyche reacts to Madness and Sadness in general. You know, Finn has a very proactive and kinda aggressive personality - and you add Crown-induced-Madness-and-Sadness and a compulsion to use Ice Magic as much as possible and you get all of…. this
Meanwhile, for Simon, the compulsions of the Crown originally filtered exclusively via the language of protection
As his madness always manifested as romantic obsession
And using goofy humor to try and deny the pain he’s going through
Because that’s how Simon’s mind specifically reacts to being flooded with so much Madness and Sadness.
That’s why there’s so many parallels between Ice King and the sort of mistakes and screwed-up stuff Simon does right now! He’s even kidnapping people again!
Because the Madness and Sadness of Ice King might’ve been induced by the Crown, but now Simon has plenty of personal home-grown Madness and Sadness inside him - and it’s no surprise that Curse-Induced or not, his mind reacts to it in a sorta-similar way. (Although obviously not as intensely, again, there was a LOT of MMS in the Ice Crown).
Now as for Ice Thing, and the fact that he seems to be actually rather well-adjusted under effects of his version of the Wishing Crown. I mean... not by the time of the 1000+ Era, but that’s literally eons in the future and also maybe more Gibbon’s fault. Even if the Crown will eventually take some sort of toll on him, for now he seems to be doing pretty well considering his wish. I mean, there's still some sort of Loss of Identity stuff going on
But everything we've seen of Ice Thing (in the present day, at least) shows him as a friendly and cheerful individual that gets along well with others. A far cry from how maladjusted every single wielder of the Ice Crown acted.
At the very least, if there's any notable amount of Sadness in him, we really haven't seen it yet.
There might be several factors here:
First things first, I should acknowledge the possibility that it’s just that Orgalorg’s eldritch brain is better at intaking all that MMS juice. That could play a part, but I think it’s probably more important, at least thematically, to look at the distinction between ‘I wish to be Evergreen’ and ‘I wish to be Ice King’.
First in the sense that while Ice King was occasionally mean to Gunter at times - he was generally much kinder than Evergreen ever was for ‘his’ Gunther. So, like, pretty much the one Personality Flaw of Ice King that you can directly link to the Ice Crown’s attempt to mimic Evergreen is the occasional anger issues.
And how they relate to Gunther’s view of Evergreen, so grumpy and controlling and constantly saying ‘NO!’
(Both Finn and Simon’s demonstrable not-crown-induced trauma responses can make them pretty short-tempered as well. So I’m not going to say this is purely the effects of the Crown. It still probably plays some sort of factor at why the wielder of the Ice Crown is Like That).
And that is not a factor in how Gunter views Ice King. For him, Ice King was a doting and loving father figure - so if the Crown was ever trying to implement any sort of specific negative personality traits, this is absolutely no longer a factor. Because the original Ice Crown was a reflection of Evergreen’s abuse, and now Ice Thing is a reflection of Ice King’s fatherly love.
Which is, itself, probably an echo or remnant of Simon’s own strong parental instincts.
Secondly, while the Crown was trying to make the Ice King just as powerful as Evergreen…. Ice King was obviously not as powerful as Evergreen. Because he was already a second-rate copy of the Ice Elemental’s power, and because Ice King was often just too doofy to use his powers correctly and probably because some remnant of Simon’s original sensible self is subconsciously holding his powers back.
Either way, being ‘like Ice King’ as Gunter sees him requires less Magic than being ‘like Evergreen’ as Gunther saw him - and therefore less Madness and Sadness. Leading to the wearer or, um, the eater being a lot more well-adjusted from the get-go.
And I think that the implication that Ice Thing has fused with the Crown, so there's never going to be another poor sap who puts on the Crown and gets Ice King'd. But if there is one somehow... at least the process is going to be less mentally detrimental that time around?
Maybe one day Simon could look back and appreciate how much he (or Ice King, or both of them, or however you want to look at the situation) is responsible for basically neutralizing the Crown that ruined his life in the first place.
