If you could change one thing about this job, what would it be?

A good answers shows you understand the challenges of this job but at the same time keep a positive additude about it and are looking for solutions. When applying for a job as investment banker you might say things like 

"Investment banking is known for its demanding hours. If I could change one thing, I would focus on making processes more efficient so that teams can work smarter rather than just longer."  

"Investment banking relies heavily on data and analysis, but many processes are still quite manual. If I could change one thing, I would push for greater investment in technology to automate repetitive tasks like financial modeling and presentation creation"

or 

"If I could change one thing, it would be to enhance mentorship and structured learning opportunities for junior bankers. The role is fast-paced and demanding, and having a more structured approach to coaching could help young professionals develop faster, take on responsibility sooner, and ultimately contribute more effectively to the team."