I don’t try and directly compare them, as ABBA was very much a product of their time. And to be perfectly fair, ABBA produced more than a few excellently-crafted, musically complex songs, such as SOS, The Winner Takes it All, and Knowing Me, Knowing You, to name a few (and certainly not to take anything away from some of the better offerings of Roxette).
Agree it is hard to compare the two, but it is inevitable given they are both Swedish. ABBA’s body of work is smaller given the relatively short time they were together. They were a shooting star that reached commercial heights that Roxette never matched.
I prefer Roxette primarily because of their lyrics and melancholic sound. They seemed more authentic and less programmatic. I also enjoy ABBA. It is not a zero sum game. Sad day for music.