Originally Posted by
Kuwagaton
They are a CLAN.
I see the Avengers as a superhero team. They're co-workers, who are rarely in each others' lives personally, and often have the veil of identity between them. They are "too" fluid and membership comes and goes on a whim. They are mostly professionals, but typically as independents; they often don't mesh and goof around in training.
I see the Fantastic Four as a family, a single family unit. They're rather stagnant. They are a group of heroes connected by real relationships, but lack the dysfunction and adversity necessary to force growth and change. From what I've seen of the foundation, it's removed from the lives of the recruits, and apparently that idea isn't even around anymore.
The X-Men started out remarkably bland, but they built up a decent rogues gallery and added acquaintances and other members. Then All-New, All-Different happened. The cast not only exploded with diversity (by mid '70s standards especially) but the book greatly increased in terms of drama. The original cast was allowed to grow from teens to adults, and the new players were being fleshed out in ways unlike other teams.
Wein, Byrne, and Cockrum made huge contributions early on, but this was largely Claremont. He wrote compelling sagas that followed one after another excellently, adding tension and raising the stakes each time. The words in the page were a smooth, warm, stream of clever purple. Women (not woman) were finally allowed power physically, emotionally, and in function, but it's hard to imagine anyone smelling an agenda. Cyclops, Wolverine, Colossus, and Nightcrawler were very much written in a way that allowed them to be favorites. The team was a family of individuals drawn together. They were underdogs, which is always fertile ground for a protagonist. The adversity they faced reflected what many of us go through, sometimes directly, sometimes as allegory. Members moved in and out, but that bond stuck. The characters were in each others' lives for better or worse.
But the action wasn't spared in the least, it was as poetic as the drama. There were stories that led from the middle of Scotland to Chicago to New York and then way out into space. The X-Men were a clan, they grew as individuals while they learned to move and fight as a unit. It was just always going down, in the 16 years Claremont was at it. Fall of the Mutants still makes my freaking day.
After Claremont, everyone was/is "sort of" Claremont. He was the X-Men and so his flavor stayed throughout the decades across multiple new titles and adaptations. Some blatantly try to evoke his power, and sometimes that works well because there were just so much fuel and momentum. He's even come back, to varying degrees of critical and commercial success, and failed to top himself. We all just know what they can be, and how they can touch us, and we're willing to keep up.