Correct, boards are an easy screen for us an a great way to start to narrow down the 2000 applications we get (for 12 spots). With this we narrow it down to 500-1000. From here we do the nitty gritty of reading LOR's, Deans letters, MSPE's, etc. From these we narrow our pool down to around 300 people, and start extending invites, with a goal to interview about 150 people for our 12 spots. Those 150 all look very similar when it comes to their boards, LORs, grades, comments, etc.
So now it's interview time. That's how the 150 determine if they're ranked #1, or #150. It isn't actually that black and white, the above still play a role. We will take the guy with a 260 on Step 2 and a "normal" interview over the person with a 215 and a really good interview. Stellar interview? You're above the 260 guy. You're the 260 guy but interview like a rock? You're gonna be below the 215 with a good interview.
We take rotation comments very seriously. Almost no one ever gets bad comments, those are an automatic red flag. Mediocre comments make us wonder if it's the applicant or the attending, but the interview normally sorts this out. As does a trend in your comments.