I was also lucky enough to see the original cast of Book of Mormon, and was generally aware of the hype around it at the time. Although I wasn't living in NY, and I wasn't as tuned into the theatre community as I am now. So I might be wrong about this, but my impression is:
Yes, at the time, the closest point of recent comparison was Book of Mormon. But in retrospect, I think the Hamilton hype was notably greater. The BoM hype was exceptional, yes. But Hamilton-mania, to me, felt different. It was like a frenzy, a mad obsession that broke out into the mainstream in a totally different way.
To illustrate just one piece of anecdotal data:
--I did SRO for Book of Mormon a couple months after the Tonys. I got to the SRO line around 9am on a 2-show day, and just missed the cut for the matinee. We kept our place in line, so we'd be right in the front for the evening SRO, and we got it. Both lotteries that day had several hundred people there. As far as I could tell, there was no cancellation line. We were there for about 11 hours.
--At the height of Hamilton's popularity, there were people waiting in line for full-price cancellation tickets for as long as FOUR DAYS. Especially right before the original cast left. On one of the in-person Ham4Ham Show days, the lottery attendant announced that there were something like 1,200 lottery entries.