At my T30, the same general group of people took up all the interview slots for virtually every OCI employer. With few exceptions, every person in the group was on some type of journal. Law review members were over-represented in that group. This may not be true at a T6, but the farther down the rankings you go I believe a journal becomes necessary for finding a job at OCI. It's not sufficient, but probably necessary. Lots of people do externships and journal at the same time too. If you are getting class credit, the two aren't mutually exclusive.
And from the people I know on law review who didn't do OCI, law review helped in their interviews with DA offices, smaller firms, and other government agencies.
Also, I'm not sure how writing the note/comment wouldn't help you in a legal job. I mean you sit down and do a ton of research on a distinct legal issue, formulate an argument, and then present the argument as clearly and persuasively as possible. You rely a little more on law review articles and theory than you would in a memo or brief, but the general process of research in writing is the same. And cite checking really does force you to pay strict attention to detail, which should also help in your career. Though I haven't worked in a legal job beyond my 1L summer, I agree with Nealric that being on the journal provides some valuable skills. If nothing else, it shows employers you volunteered to spend long hours on legal work outside of required class work.