I think that the biggest proof that most Martin fans don't understand Martin is that they never write him really being jealous or bitter. Not like he is in the show. They just make him sad and self-sacrificing and skim over his obvious dislike and disregard for most other people. He's rude to people who don't get along with Jon, with people who get along with Jon too well, and also Jon himself. The first time we hear him, he spends a bunch of time passive-aggressively guilting Jon for Martin getting trapped by Prentiss. Melanie and Basira joke about how rude Martin is to them because of their relationships with Jon. Martin effectively burned his friendship with Tim by acting like a mediator while showing obvious bias. He's such a dick, which I find really funny and apparently no one else does.
“He’s rude to people who don’t get along with Jon, to people who get along with Jon too well, and also to Jon himself” dear GOD you’re so right. It’s like he’s simultaneously insecure and egocentric.
From what I’ve gathered, this is caused by most fans seeing themselves in Martin. Most of their time is spent piling their own personality traits onto the man, instead of trying to understand him as he is.
The fact people prefer the popularized fanon version also adds to this. In fanon he’s a loving, caring, protective sweetheart. His biggest flaws are that he hates himself and loves too much; both perfectly harmless and relatable. There’s nothing that might make him seem unredeemable, his every trait is perfectly innocent and excusable. Sweet gay tormented blorbo.
Martin isn’t the only one who fell victim to the fandom oversimplification to be honest. Jon’s either the mean stubborn idiot or a soft and helpless gayboy who needs his boyfriend to care for him. Tim is the comic relief funny guy who’s only there to goof, and Sasha is the smart one who’s also secretly a prankster. Daisy is the Bad Cop violent butch and Basira is the Good Cop cool-and-collected hijabi. Elias is the flamboyant evil boss and Peter Lukas is his bitter sugar daddy do you see it do you see what I mean. That’s the fandom making them more digestible and versatile so that they can fit them into fanfiction tropes. This is a common occurence in every fandom but it’s sooo prominent here and dear god I hate it. Downsides of a fandom peaking in 2021