I would say that the best FAIR comparison is comparing "Unbreakable" to "Rebel Heart"'s 1st week. 31 years later, pushing 50, to TOP the album charts in 2015 with 108k albums is AMAZING.
Madonna ended the week with 110k who is arguably the biggest pop singer of all time so Janet is right on par with HER legendary self also.
Comparing the 1st week to Tamar is a lil unfair to Tamar because she sucks really big floppy donkey d*ck and isn't even surpassed "amateur" status, let alone the MILES and GALAXIES away from being considered a legend.
Go on Janet!