and the M.A.N.T.I.S.
Bias that I may have for him for being in BSG as well, I can safely say he was one of my favorite parts/characters of the movie. Wasn't he voice of Martian Manhunter too in the Justice League cartoons way back when?
Adamantium was never a macguffin in this movie. It was just the impetus for the international treaty Ross was trying to pull together as his legacy to change the world for the better.
Which he successfully did, in the end, once he stopped trying to justify his past and just owned up to his shit.
I'd argue the Adamantium was more a macguffin for the plot than central to the story of the film. We didn't really see anything interesting, or impactful story-wise relating to this newly-discovered-indestructible-metal-that-maybe-has -military-applications-if-we-can-figure-out-a-way-to-coat-someone's-skeleton-with-it-and-give-them-extendable-claws. We were shown a few exposition scenes with dialogue to tell us adamantium exists, and it is important. You can say Adamantium was impetus for development of an international treaty in the film, yes, but that does not mean it was central to the story of Captain America, Thunderbolt Ross, Red Hulk, or any character in the movie, really. I would also clarify that Ross' motivation was two-fold: his personal desire to rebuild his fractured relationship with his daughter as he faced down his own mortality, and protecting the image of his presidential legacy to help with the former.
It's theft in the beginning leads to a situation that gets all of our characters off to the White House for a meet and greet and Ross' attempted assassination. This drives Sam Wilson to look into things and creates the diplomatic tension the plot needs between Ross and Japan to keep things going, but we don't see anything important being done with adamantium. It's presence in the film doesn't really add much to enrich the story or the MCU at large, other than culminating as the driving force behind an orchestrated international crisis that ends up being narrowly avoided.
At the end of the movie, Ross' legacy is questionable, international relations are status quo, we have our treaty, and Adamantium is... still just there. I am not saying that they needed to give us Wolverine or the Weapon X program to justify using adamantium, but I do think that it was primarily used 1) as a general reference to get a like or two from comic book fans who would be excited at the name drop, and (2) a macguffin to drive the plot until we get to our big twist with the Leader, the gamma pills, and Ross/Red Hulk. Then we wrap things up with our big showdown with Red Hulk and Captain America, topping it off with the opportunity for Ross' redemption. Fin.
The previous theft/discovery/existence of adamantium hasn't added anything to enrich the movie's story, the characters, or the MCU, nor were there any real consequences other than affirming that adamantium is now officially MCU canon.
