Hi Dancy, thanks for your thoughtful comment! Your analysis of the movie was also very thought-provoking and educational 😄
When I saw the scene of Shang-Chi training with his aunt, and then later the flashback of his mom teaching him tai chi, I already predicted that Shang-Chi would use his mother's martial arts style to defeat Wenwu, so I didn't doubt that Shang-Chi would be able to overpower Wenwu.
I know you initially thought that the soul-sucker killing Wenwu was a cop-out, but I think the story writers could have easily just had Shang-Chi overpower Wenwu and take away his rings and then lock him up without killing him. So I think having the soul-sucker kill Wenwu was to show that Wenwu regretted his mistake and wanted to make his last moments something he didn't regret, which was to pass his legacy (rings) to his son, thereby telling him "I love you, I'm sorry for my mistakes, I believe you have matured now, and I hope you will use the rings to protect our family."