Theres something for everyone so it’s not fair to say someone’s overrated.
That said I don’t trust modern music sales figures because if you’re rich and powerful, and backed by a strong label they can be manipulated. Taylor’s latest album is available on 19 different formats, this includes multiple different album covers and versions where there is a different bonus track. Her most rabid fans will buy every version pushing up sales. Meanwhile Adele’s biggest album came in one version on 2 formats. Her record were almost entirely individual purchases.
In addition, Taylor’s people game Spotify by ensuring her songs are inserted into random ‘you may also like’ Playlists. Therefore you could select Travis Scott and within 30 mins a Taylor Swift song will appear. These artists are nothing alike. This will be counted as a stream/sale.
The charts are fake and just used as a marketing tool by those with the power to do so. It’s not like the 80s/90s where you had to go in the store and buy a physical album. I don’t believe she’s sold anywhere near as many records as people like Madonna or Michael Jackson at all but her figures back up the hype meaning her tours sell more and that’s where the real money is. You have to hand it to her marketing team.