Why not a ranking based on what a school actually does. For private schools the most important ranking is probably average starting salary of graduates or rate of return on student investment. Private schools, after all, do not exist because of the rationale that legal education is a public good. I understand that not every student attending a private school takes the highest paying job offer but, a clean ranking by starting salary, adjusted for cost of living, would at least isolate what many students are after. Plus, if the graduates are really that good, presumably they would be made private sectors job offers they can not refuse.
For public schools why not number of graduates taking public sector jobs or practicing in firms with 5 attorneys or less. Public schools students are subsidized at one level or another because someone somewhere along the line convinced people that legal education is a public good. (And not, as I think, a method of income redistribution from lower ranks to higher ranks.) If it is manufactured at inefficiently low levels it must be because the prices in the market do not reflect the true value. So why not measure the public schools by the number people who actually do something other than attempt to fully internalize the benefits of an education someone else contributed to. I know the subsidization varies from school to school so we would work out some kind of ratio.
I am personally not that keen of bar passage rate being goal of every law school but I understand the vast majority of students do take the bar and hope to practice law. But bar passage rate tells you very little. For example, suppose you are a student with a 3.5 GPA and a 150 on the LSAT. Is it bar passage rate that is important or is it bar passage rate for students like you? An informative bar passage measure is one that accounts for different qualifications of entering students. Most students with a 4.0 and a 178 will pass the bar at any school. The idea that schools that primarily admit these students also get credit for a high bar passage rate makes no sense at all.
I can think of other measures but they all come down to a School deciding what its role is and then measuring its success. This is very different from what typically goes on: A faculty examines what its school does and then decides that those are its goals and gives itself an A. My sense is that the only thing good about USN&WR report is that it takes the rankings out of the hands of complacent faculties and administrators who serve them.