The OP doesn't work in tax. He works for a bank.
Even if true, which I doubt, that still doesn't explain why you would compare a certification (14 hours of testing and work experience) to an advanced degree (years of learning and tens of thousands of dollars).
The OP said he's not sure what he wants to do and your suggestion is to spend tens of thousands of dollars to learn a specialty?
I don't follow how a Tax LLM or MST for that matter translates to finance?
His background is in finance not accounting.
Sure, but that isn't what the OP asked. This is also a completely different career path than the one he just started.
I still don't get what a law degree in tax has to do with top finance jobs?