The MCU has turned out to be a largely successful universe. This is not to say that there weren’t any bumps in the road or wrong turns. A lot of these bad turns were made with the Iron Man solo films. The ironic thing about this is that the first Iron Man was a really good entry in the MCU. However, the second and third Iron Man movies disappointed. The greatest disappointment came with Iron Man 3 when they were bringing the Mandarin to the big screen. One of the most disappointing aspects of this film was they built him up to be a very dangerous villain only to show him to be a goofball act.
People were so disappointed with this approach that Marvel has decided to release a one-shot showing that the actual Mandarin is out there in the MCU yet to be used. The interesting thing is that he was often associated with Iron Man. Robert Downey Jr’s contract for his role in the MCU is almost complete. Therefore, it is very likely that the real Mandarin is not going to be pitted against Tony Stark. However, Spider-Man might be the one to take on the Mandarin in a future movie since he shares a close relationship with Tony Stark.
Of course there are plenty of other missed opportunities in the MCU. This includes certain stories that had to be scaled down. One of the reasons behind these missed opportunities is that the movie rights to the Marvel characters have been split throughout plenty of studios. If all of the movie rights were with one studio, then it would’ve probably taken a while to tell some of the stories that have been told in one movie.