An underlying skill set for both professions is sales ability. Law partner spots are very limited and are based on the ability to gather clients, not pure legal ability. Investment Banking IS sales. One reason bankers are paid so well is that it is hard to find individuals who can sell and do finance analytics.
Without an affinity for sales, you can make a decent living (not great) in law if you do well in law school and go to a top 50 school. If you can't sell, you will never make it as an investment banker.