Changed my answer.
YES TAYLOR IS AND will be the most successful artist of the decade.
i checked from my source regarding the stats I posted and they were just for songs not albums.
So yes
Taylor will win.
Katy will be rank #1 in songs and digital
Adele might be able to do it WW if she can release a smash this era and another album by 2019.
Overall, it's Taylor.
How could i doubt the power of blonde female icons
80s- Madonna
90-Mariah
00s-Britney
10s-Taylor