A lot of people put investment banking on their linkedin but has never been an investment banker.
#2 doesn't sound too good because:
1) 6 month will get you to just before year end. Unless it is an automatic conversion, they will likely need to create a new requisition to convert and many banks lock their hires Q4.
2) You are pretty much guaranteed to be doing grunt work. No one will bother training you up. Big 4 at least you have internal support and assignments can often be longer term.
3) Having to work knowing you have a 6 month window can be very stressful.
I suggest you find out more about what kind of consulting you will be doing in Big4.
The guy used to work at US and Euro investment banks and lasted as Executive Director. The pattern of his profile is as such: US > Euro > now Singaporean bank (mix of consumer banking and i-banking). Agreed that there's a clear deteriorating pattern with the banks he was with.
To your last point, I work on finance and system transformations in Big 4 consulting.
I think your choices are pretty clear then. I suggest you go with 1). The high paying data scientist jobs you saw on glassdoor are really software engineering specializations. The work that you will be doing for the Singaporean bank will not help you become a data scientist.
Are you an expat yourself? And I assume your friends/ex-colleagues are too?
Guess they all felt turned off by those 48-58k jobs then?
What expat-specific platforms or agencies do they use in order to avoid those local job calls?
I would imagine it's difficult if you were not working in investment banking which is supposedly filled with most expats by observations.