Yeah but...did they write the original songs? Did they reinterpret them with new instruments? Or are they all samples from original content?
Like take an 8bit cover of say...My Heart Will Go On, even though they didn't write the original song, at least they made an attempt to completely overhaul it with a different set of instrumental tools.
I'm not so much of a snob that I discredit computer created music as non musical. But...I see mashups as a novelty thing, much like (adding something I happen to love) Happy Metal's Major Key transformations of minor key songs. It's neat, and may have technical prowess behind it, it's still not an original creation.
This point of view extends to cover songs as well. Novelty, and can be done differently, but still not original.