Iron Man (Robert Downey Jr.) should not have met his daughter Morgan in the Soul World in Avengers: Endgame's cut scene. Instead, he should have met Ho Yinsen (Shaun Toub) again. Directors Joe and Anthony Russo attempted to recreate the Avengers: Infinity War moment where Thanos (Josh Brolin) sees a young Gamora (Arianna Greenblatt) in the Soul World after the snap. However, it didn't have the same impact as its predecessor, resulting in the film creatives opting scrap it altogether.
After a couple of brush-up with death in the Avengers' fight against Thanos in Infinity War, Tony decided to totally walk away from his role as a superhero and focused on his personal life. He made good with his promise to marry Pepper Potts (Gwyneth Paltrow) and in the five-year time-jump after the decimation, the couple built a quiet family life together with daughter Morgan Stark (Lexi Rabe). However, when duty called again once the idea of the time heist came up thanks to Scott Lang/Ant-Man (Paul Rudd), Tony was forced to come out of retirement with the goal to bring back those who perished in the snap — particularly Tony's mentee, Peter Parker/Spider-Man (Tom Holland).
In the end, Tony decided to sacrifice his life for the greater good, wielding the power of all six Infinity Stones to take down Thanos and his minions once and for all. Like the Mad Titan in Infinity War, he was supposed to have a reunion with his grown-up daughter, but between the removed dialog and the audience's unfamiliarity with Langford as Morgan, the scene didn't resonate as intended. The Russos decided to cut the Soul World scene altogether, but they didn't need to get rid of it totally as it would have worked if they featured Yinsen with Tony instead of Morgan.
In Thanos’ Soul World scene in Infinity War, young Gamora forces him to re-examine his quest for the Infinity Stones and the lengths he went to for his crusade. Deep down, the Mad Titan knew that her adopted daughter was against his mission, but he was so convinced of his calling that he was still sold on the idea that the genocide he committed was an act of bravery on his part. Yinsen could’ve provided the same thing for Tony as he’s the reason why he survived his kidnapping in Afghanistan in 2008. The brilliant surgeon also opened his eyes to how his creations were being used against the very people they were supposed to protect, directly motivating him to be personally involved in any way he can as Iron Man.
Yinsen's life and actions forever changed Tony's perspective; the genius, billionaire realized that he can do more good than creating weapons and profiteering from war. While their time together was brief, Yinsen arguably had the biggest impact on Tony's life than anyone else and his sacrifice at the end of Endgame could have mirrored what Yinsen did to save Tony in Iron Man. Reuniting the pair in the Soul Stone would've been the perfect way to bring Tony's arc full circle as they conversation could be about how Tony turned his life around and not waste it as Yinsen advised him just before he died.
Marvel Studios impressively stuck the landing in Avengers: Endgame, which was no easy feat considering the string of disappointing finales fans have had to endure in the last few years. That said, it was a massive missed opportunity to not to bring back Yinsen into the MCU considering how pivotal he was in Iron Man's heroic journey.