The MCU is ready for another big Avengers leader akin to Tony Stark, and that character himself proves why Ikaris from Eternals would have been a great choice. With both Tony and Steve gone, the Avengers are in need of a new leader, and there are some good heroes to choose from. However, it is Ikaris' similarities to Tony that would have meant he was a great option for the role.
Ikaris' narrative in Eternals saw him transform from a respected leader to an antagonistic betrayer of his family. All along he knew of the emergence and its destruction, and whilst his family sought a way to stop it happening, he stayed loyal to Arishem's mission and believed it was actually for the best. It is this determined attitude to do what he thinks is right which proves he could have been a good leader to follow Stark's legacy.
Tony was a great leader because of his faults. He began life in the MCU as a self-important arms dealer who didn't care for the consequences of his actions. Throughout the films, he grew into someone with a big heart who would do whatever was needed no matter the cost, even sacrificing himself for the greater good. In spite of backlash from their found families, both would each do what they truly thought was the right thing. Not to act as an antagonist, but to uphold their personal belief system and try to keep those they love safe.
Tony believed he was right in Captain America: Civil War and went head to head with Steve, each willing to fight for what they thought was best. Tony wound up imprisoning those he called his friends, because he was sure it was the only way to keep people safe. Despite his misguided routing, he only had good intentions in his heart. This is especially similar to Ikaris in Eternals. He believed the emergence was part of the natural order, and by preventing it from happening, it could cause catastrophic damage to the universe. Despite his betrayal as the film's biggest twist, he simply believed that it was the best thing to do. Ikaris' ending, flying into the sun, also shows his willingness to sacrifice, much like Tony.
It is this fierce determination showcased by both Tony and Ikaris that would have ensured the latter had the potential to be a great leader to the next generation of heroes. Ikaris, like Tony, could have had room to grow and learn from his mistakes, making him a more well-rounded individual. Eternals was only the beginning of Ikaris' story, and despite his hubris, he could have learned to be better.