True. I think the whole 21 album would've been just as, if not more huge say, 40 years ago. It's definitely a timeless album.
BTW, I think most of the songs from Beyonce's 4 would've had more success in decades past than now, owing to the fact that the overall music climate of today isn't so open to R&B as 20 years ago or earlier.
Janelle Monae DEFINITELY would've been huge in the 70s and/or 80s. The general public would've been a lot more open to her music, since being experimental with your music was actually something mainstream artists did back then.