dunno,
I think this is largely a myth. There is definitely an advantage in some respects, especially when it comes to analyzing a piece of legislative or constitutional text, or when trying to really pick apart the text of a court decision to support your arguments.
However, the way we learn gemara is in many ways antithetical to how we study and practice law in America. In learning gemara, there is of course a stress on understanding the CORRECT LAW. In law school, we study not so much to understand what the law really is, but more to see how we can use the existing state of the law to support a particular position. The secular-law idea that there isnt really an objectively correct law, but that there is a body of rules, standards, and precedents that we try to analyze and use to our advantage in practice is very foreign to most yeshiva students who have learned God’s law for the sake of simply knowing the right thing to do.
Even to the extent that genera learning helps for general skills needed to study law, american law study and practice is more and more dependent on excellent writing skills – command of the language, preciseness, clarity, ect. Sadly, many BTL guys lack these skills and have a hard time managing both legal writing classes and writing exams.
This isn’t to say there aren’t exceptions – there are, and I have seen them; and I am not speaking based on empirical evidence – just my personal observations. Learning gemara definitely helps develop many of the raw mental qualities that serve a law student well, but often they are just that – raw qualities. Many college students are better prepared in other essential areas (again, I am generalizing). I think both College and BTL students have advantages – each one has different ones, though – and I don’t think it is accurate to say that BTLs have any overall advantage. I think the opposite is true in most cases.