Omfg not at all
In 2014, yes and considering she has no competition right now, it's probably the best one of 2015 but the entire decade?? Mainstream music in terms of both quality and sales were amazing at the beginning of the decade and started to decline around 2013. 21, Teenage Dream, Loud, even her own Red and Speak Now, Doo Wops and Hooligans, Unorthdox Jukebox are just a few of the many albums I can name off the top of my head that are all miles better than 1989.
In comparison to mainstream music currently, it's the best option but compared to five years of music...