You're correct, he came out of a new mutants arc, back about 40 years ago. He did also eventually get a solo series, as well as sort of a team series, but those were much later, and certainly not where the character came from. He was just a character that would occasionally pop up in X books for many years before actually having a book. Unless the other person was more just saying the character came from A comic book series, not specifically a Legion one.
But anyway, X-Men Legacy (Vol. 2, 2012) was basically a Legion solo book. Si Spurrier wrote it, had 25 issues, and was a lot of fun.
Then Si Spurrier returned to write Legion of X, well into the Krakoan era. Was basically a team book of Legion, Nightcrawler, Juggernaut, Pixie, and maybe someone else? Legion and Nightcrawler were definitely the main character focuses though.
Neither resemble the tv show in any way.
While I haven't played D2 in years, I think you're missing a LOT of the content that it does have. Sure, a seasonal storyline may be small, with a proper expansion campaign being a little longer, but if you really get into Destiny, finishing that stuff is just were the game starts. From there you have raids, dungeons, crucible, gambit, trials of the 9, whatever the seasonal activity is, grinding out long weird questlines to get a particular exotic, doing hidden jumping puzzles to get a different exotic, etc. etc.
Definitely fair that it hooked you less and thus you didn't get into all that other content, but objectively, Destiny did have a fuckton of content.