Hiii Club, congrats on your offer!
Underwriting itself is actually quite a decent career pathway. You need not to worry about your career progression as there are so many giant re-insurance companies in Hong Kong which are hiring for different levels of staff.
I guess it can help in your CV, as at least these are FIs (financial institutions) but not directly related to Banks' major functions. All in all, it is more important for you to have better academic results in order to pass through the screening of Banks' and Regulators' MT Programmes. Of cox, it will be much better for you to gain direct intern / part-time / placement exp in those organizations. More importantly, are there other better offers that are more related to your ideal industries? If no, it is always good to have more internship exp as a whole.
Oh right, you may want to have a look on the career progression of a career in underwriting as well:
Hope it helps!